Filed pursuant to Rule 424(b)(3)

 Registration No. 333-261740

PROSPECTUS SUPPLEMENT NO. 1

(to prospectus dated May 3, 2022)

Up to 8,927,528 Shares of Common Stock Issuable Upon Exercise of Warrants

Up to 90,477,403 Shares of Common Stock

Up to 3,177,542 Warrants

This prospectus supplement is being filed to update and supplement the information contained in the prospectus dated May 3, 2022 (the “Prospectus), related to the issuance by us of up to an aggregate of up to 8,927,528 shares of our common stock, $0.0001 par value per share (“Common Stock”), which consists of (i) up to 3,177,542 shares of Common Stock that are issuable upon the exercise of 3,177,542 warrants (the “Private Placement Warrants”) originally issued in a private placement in connection with the initial public offering of DFP Healthcare Acquisitions Corp., a Delaware corporation (“DFP” or “DFPH”), by the holders thereof, and (ii) up to 5,749,986 shares of Common Stock that are issuable upon the exercise of 5,749,986 warrants (the “Public Warrants,” and together with the Private Placement Warrants, the “Warrants”) originally issued in the initial public offering of DFP, by the holders thereof. We will receive the proceeds from any exercise of any Warrants for cash.

The Prospectus also relates to the offer and sale from time to time by the selling securityholders (including their transferees, donees, pledgees and other successors-in-interest) named in the Prospectus (the “Selling Securityholders”) of (a) up to 43,178,072 shares of Common Stock issued to certain former stockholders of TOI Parent, Inc. in connection with the Business Combination (b) up to 16,967,747 shares of Common Stock by certain of the Selling Securityholders (as defined below) in connection with the PIPE Investment, (c) up to 16,351,042 shares of Common Stock issuable upon conversion of any Series A Common Equivalent Preferred Stock (including 10,000,000 shares of Common Stock underlying shares of Series A Common Equivalent Preferred Stock issued in the PIPE Investment), (d) 9,372,540 Earnout Shares issuable to certain former stockholders of TOI Parent, Inc. pursuant to the Merger Agreement, (e) 3,580,063 shares of Common Stock underlying options held by certain directors and officers of the Company, (f) 696,000 Earnout Shares issued to certain directors and officers of the Company and and (g) 331,939 shares of Common Stock issued to former directors and officers of the Company prior to the Business Combination. We will not receive any proceeds from the sale of shares of Common Stock or Warrants by the Selling Securityholders pursuant to the Prospectus.

This prospectus supplement updates and supplements the Prospectus with the information contained in Item 5.02 of our Current Report on Form 8-K, filed with the Securities and Exchange Commission (“SEC”) on May 5, 2022 (collectively, the “Information”). Accordingly, we have attached the Information to this prospectus supplement.

This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement. We are an “emerging growth company” as defined in Section 2(a) of the Securities Act of 1933, as amended (the “Securities Act”), and are subject to reduced public company reporting

requirements. This prospectus supplement complies with the requirements that apply to an issuer that is an emerging growth company.

Our Common Stock and Public Warrants are listed on the Nasdaq Stock Market LLC (“Nasdaq”) under the symbols “TOI” and “TOIIW,” respectively. On May 6, 2022, the closing price of our Common Stock was $8.81 and the closing price for our Public Warrants was $1.30.

We will bear all costs, expenses and fees in connection with the registration of the shares of Common Stock. The Selling Securityholders will bear all commissions and discounts, if any, attributable to their sales of the shares of Common Stock.

See “Risk Factors” beginning on page 7 of the Prospectusto read about factors you should consider before investing in our Common Stock or Warrants.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is May 9, 2022.

Item 5.02    Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

As previously announced, The Oncology Institute, Inc. (the “Company”) and Scott Dalgleish, the Company’s former Chief Financial Officer, reached an agreement (the “Separation Agreement”) to enable Mr. Dalgleish to transition out of the Company to pursue other opportunities. Mr. Dalgleish’s last date of employment with the Company was April 29, 2022. On April 29, 2022, the Company entered into a consulting agreement (the “Consulting Agreement”) with Mr. Dalgleish, effective as of April 30, 2022, to retain Mr. Dalgleish as a consultant until May 31, 2022 (unless terminated earlier pursuant to the terms of the Consulting Agreement). Pursuant to the Consulting Agreement, Mr. Dagleish will be eligible to continue to vest in up to 15,183 of his outstanding stock options, and the post-termination exercise period of his stock options was extended through December 31, 2022.

The foregoing is a summary of the material terms of the Consulting Agreement. The summary does not purport to be complete and is qualified in its entirety by reference to the Consulting Agreement, which will be filed as an exhibit to the Company’s Quarterly Report on Form 10-Q for the fiscal quarter ending June 30, 2022.