Exhibit 5.1

Board of Directors Marvell Technology Group Ltd. Email   MEBrewer@applebyglobal.com   Direct Dial   +1 441 298 3226   Tel   +1 441 295 2244 Fax   +1 441 292 8666   Your Ref   Appleby Ref   124194.0045/ME/SS   19 July 2018

  Bermuda Office   Appleby (Bermuda) Limited   Canon’s Court   22 Victoria Street   PO Box HM 1179   Hamilton HM EX   Bermuda   Tel +1 441 295 2244   applebyglobal.com Dear Sirs   Marvell Technology Group Ltd. (Company)   INTRODUCTION   This opinion as to Bermuda law is addressed to you in connection with the filing by the Company with the Securities and Exchange Commission under the Securities Act of 1933, as amended (Securities Act) of a Registration Statement in relation to a Post-Effective Amendment No. 2 on Form S-3 to Form S-4 (Registration Statement) with respect to the issue by the Company of Common Shares (Shares) (as described in the Registration Statement, and collectively referred to as Shares Offerings).   OUR REVIEW   For the purposes of giving this opinion we have examined and relied upon the Registration Statement and the documents listed in Part 2 of Schedule 1 to this opinion (Documents). We have not examined any other documents, even if they are referred to in the Documents.   For the purposes of giving this opinion we have carried out the Company Search and the Litigation Search described in Part 3 of Schedule 1.   We have not made any other enquiries concerning the Company and in particular we have not investigated or verified any matter of fact or representation (whether set out in any of the Registration Statement or elsewhere) other than as expressly stated in this opinion.   Unless otherwise defined herein, capitalised terms have the meanings assigned to them in the Registration Statement.

Appleby (Bermuda) Limited (the Legal Practice) is a limited liability company incorporated in Bermuda and approved and recognised under the Bermuda Bar (Professional Companies) Rules 2009. “Partner” is a title referring to a director, shareholder or an employee of the Legal Practice. A list of such persons can be obtained from your relationship partner. Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

LIMITATIONS

Our opinion is limited to, and should be construed in accordance with, the laws of Bermuda at the date of this opinion. We express no opinion on the laws of any other jurisdiction.

This opinion is strictly limited to the matters stated in it and does not extend to, and is not to be extended by implication, to any other matters. We express no opinion on the commercial implications of the Documents or whether they give effect to the commercial intentions of the parties.

This opinion is given solely for the benefit of the addressee(s) in connection with the matters referred to herein and, except with our prior written consent, it may not be transmitted or disclosed to or used or relied upon by any other person or be relied upon for any other purpose whatsoever, save as, and to the extent provided, below.

We consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement but it is not to be made available, or relied on by any other person or entity, or for any other purpose, nor quoted or referred to in any public document nor filed with any governmental agency or person (other than the SEC in connection with the Registration Statement), without our prior written consent except as may be required by law or regulatory authority. As Bermuda attorneys, however, we are not qualified to opine on matters of law of any jurisdiction other than Bermuda, and accordingly do not admit to being an expert within the meaning of the Securities Act.

ASSUMPTIONS AND RESERVATIONS

We give the following opinions on the basis of the assumptions set out in Schedule 2 (Assumptions), which we have not verified, and subject to the reservations set out in Schedule 3 (Reservations).

OPINIONS

1. Incorporation and Status: The Company is incorporated as an exempted company limited by shares and existing under the laws of Bermuda and is a separate legal entity. The Company is in good standing with the Registrar of Companies of Bermuda.

2. Shares: When duly authorised, allotted, issued and fully paid for pursuant to the terms of the Resolutions, and any other requisite resolutions of the Board of Directors in respect of any Common Shares, and in accordance with the terms and conditions referred to or summarised in the Registration Statement and in any prospectus supplement issued pursuant to and as contemplated by the Registration Statement, the Common Shares will be validly issued, fully paid and non-assessable shares in the capital of the Company.

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

3. Shares Offerings: The Company has all the requisite corporate power to enter into, execute, deliver and perform its obligations under the Shares Offerings to which it may become a party and to take all actions as may be necessary to complete the transactions contemplated thereby.

4. By Notice to the Public published by the Bermuda Monetary Authority on 1 June 2005, general permission pursuant to the Exchange Control Act 1972 and the Exchange Control Regulations 1973 made thereunder was given by the Bermuda Monetary Authority for the issue and subsequent transfer of any securities of a Bermuda company from and/or to a non-resident, where any ‘Equity Securities’, as defined in the Exchange Control Notice, are listed on an appointed stock exchange, which includes the NASDAQ Global Select Market.

Yours faithfully

/s/ Appleby (Bermuda) Limited

Appleby (Bermuda) Limited

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

SCHEDULE 1

Part 1

The Registration Statement

1. A copy, in PDF format of the final form of the Registration Statement dated 19 July 2018, excluding the documents incorporated by reference therein.

Part 2

Documents Examined

1. A certified copy of the certificate of incorporation of the Company dated 11 January 1995 (Certificate of Incorporation).

2. A copy of the memorandum of association, certificate of deposit of memorandum of reduction of share premium dated 8 August 2011, certificates of deposit of memorandum of increase of share capital respectively dated 29 June 2006, 7 June 2004, 25 April 2000, 16 July 1999, 22 July 1998, 26 September 1996, 10 March 1995 and bye-laws of the Company adopted on 8 November 2016 and certified as a true copy by the secretary on 19 July 2018 (together the Constitutional Documents).

3. A Certificate of Compliance, dated 19 July 2018 issued by the Registrar of Companies in respect of the Company. (Certificate of Compliance).

4. A copy of the resolutions adopted by the board of directors of the Company at a meeting duly convened on 18 November 2017 certified respectively by Matthew J Murphy, a director, on 18 July 2018 and by Mitchell L. Gaynor, chief administration and legal officer and secretary, on 18 July 2018 (the Resolutions).

5. A copy of the Register of Directors and Officers of the Company certified as a true copy by the secretary of the Company on 19 July 2018 (Register of Directors and Officers).

6. A Secretary’s Certificate (Certificate) dated 28 March 2018 together with a bringdown certificate dated 19 July 2018.

7. A copy of the results of the Litigation Search.

8. A copy of the results of the Company Search.

9. A certified copy of the Foreign Exchange Letter, dated 29 May 2000, issued by the Bermuda Monetary Authority, Hamilton Bermuda in relation to the Company (Foreign Exchange Letter).

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

10. A certified copy of the Tax Assurance, dated 5 April 2012, issued by the Registrar of Companies for the Minister of Finance in relation to the Company (Tax Assurance).

11. A PDF copy of the Notice to the Public issued by the Bermuda Monetary Authority on 1 June 2005.

Part 3

Searches

1. A search of the entries and filings shown and available for inspection in respect of the Company in the register of charges and on the file of the Company maintained in the register of companies at the office of the Registrar of Companies in Hamilton, Bermuda, as revealed by a search conducted on 19 July 2018 (Company Search).

2. A search of the entries and filings shown and available for inspection in respect of the Company in the Cause and Judgement Book of the Supreme Court maintained at the Registry of the Supreme Court in Hamilton, Bermuda, as revealed by a search conducted on 19 July 2018 (Litigation Search).

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

SCHEDULE 2

Assumptions

We have assumed:

1. (i) that the originals of all documents examined in connection with this opinion are authentic, accurate and complete; and (ii) the authenticity, accuracy completeness and conformity to original documents of all documents submitted to us as copies;

2. that the Registration Statement and other documentation which was received by electronic means is complete, intact and in conformity with the transmission as sent;

3. that there has been no change to the information contained in the Certificate of Incorporation or to the Constitutional Documents;

4. that the signatures and seals on all documents and certificates submitted to us as originals or copies of executed originals are genuine and authentic, and the signatures on all documents executed by the Company are the signatures of the persons authorised to execute the documents by the Company;

5. the truth, accuracy and completeness of all representations and warranties or statements of fact or law (other than as to the laws of Bermuda in respect of matters upon which we have expressly opined) made in the Registration Statement and any correspondence submitted to us;

6. that: (i) the Registration Statement is in the form of the documents approved in the Resolutions; (ii) any meetings at which Resolutions were passed were duly convened and had a duly constituted quorum present and voting throughout; (iii) all interests of the directors on the subject matter of the Resolutions, if any, were declared and disclosed in accordance with the law and Constitutional Documents; and (iv) the Resolutions have not been revoked, amended or superseded, in whole or in part, and remain in full force and effect at the date of this opinion; and (v) the directors of the Company have concluded that the entry by the Company into the Registration Statement and such other documents approved by the Resolutions and the transactions contemplated thereby are bona fide in the best interests of the Company;

7. that there is no matter affecting the authority of the directors issue the Registration Statement including breach of duty or lack of good faith which would have any adverse implications in relation to the opinions expressed in this opinion;

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8. that the Company has entered into its obligations under the Registration Statement in good faith for the purpose of carrying on its business and that, at the time it did so, there were reasonable grounds for believing that the transactions contemplated by the Registration Statement would benefit the Company; and

9. that at the time of any issue and sale of any Shares, such Shares will be listed on an “appointed stock exchange” as understood under Bermuda law, or permission will have otherwise been given by the Bermuda Monetary Authority for the issue and if necessary, transfer of the relevant Shares;

10. that at the time of the issue of any shares of the Company which are comprised in the Shares, the Company will have sufficient authorised and unissued share capital and will hold any relevant necessary permissions or directions of the Bermuda Monetary Authority, the Registrar of Companies and/or the Minister of Finance, or such ministry’s successor (as applicable) for such issue and sale;

11. that any supplemental prospectus prepared in relation to the offer of any of the Shares, as contemplated by the Registration Statement, will have been duly authorised by the Board of Directors of the Company and will comply with and have been prepared in accordance with all relevant legislation and the Constitutional Documents; and

12. that any contracts or instruments, including but not limited to indentures and warrant instruments, prepared in relation to the offer and creation of any of the Shares, as contemplated by the Registration Statement, will comply with and have been prepared in accordance with all relevant legislation and the Constitutional Documents, and will constitute legal, valid and binding obligations of each of the parties therefore, enforceable in accordance with their terms, under the laws by which they are governed.

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai

SCHEDULE 3

Reservations

Our opinion is subject to the following:

1. Bermuda Law: We express no opinion as to any law other than Bermuda law and none of the opinions expressed herein relates to compliance with or matters governed by the laws of any jurisdiction except Bermuda. This opinion is limited to Bermuda law as applied by the Courts of Bermuda at the date hereof.

2. Enforcement: Where an obligation is to be performed in a jurisdiction other than Bermuda, the courts of Bermuda may refuse to enforce it to the extent that such performance would be illegal under the laws of, or contrary to public policy of, such other jurisdiction.

3. Good Standing: The term “good standing” means that the Company has received a Certificate of Compliance from the Registrar of Companies.

4. Non-assessable: Any reference in this opinion to shares being “non-assessable” shall mean, in relation to fully-paid shares of the Company and subject to any contrary provision in any agreement in writing between such company and the holder of shares, that: no shareholder shall be obliged to contribute further amounts to the capital of the Company, either in order to complete payment for their shares, to satisfy claims of creditors of the Company, or otherwise; and no shareholder shall be bound by an alteration of the Memorandum of Association or Bye-Laws of the Company after the date on which he became a shareholder, if and so far as the alteration requires him to take, or subscribe for additional shares, or in any way increases his liability to contribute to the share capital of, or otherwise to pay money to, the Company.

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Bermuda  •  British Virgin Islands  •  Cayman Islands  •  Guernsey  •  Hong Kong  •  Isle of Man  •  Jersey  •  Mauritius  •  Seychelles  •  Shanghai