<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>2103100 - Disclosure - Senior Revolving Credit Facility</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>D2013Q2YTD</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000863456</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-02-03T00:00:00</PeriodStartDate><PeriodEndDate>2013-08-03T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Aug. 03, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>wtsl_SeniorRevolvingCreditFacilityAbstract</ElementName><ElementPrefix>wtsl_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Senior Revolving Credit Facility [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>wtsl_SeniorRevolvingCreditFacilityTextBlock</ElementName><ElementPrefix>wtsl_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>verboseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2013Q2YTD" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family:Times New Roman;font-size:10pt;"&gt;&lt;div style="line-height:120%;padding-bottom:12px;padding-top:18px;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-weight:bold;"&gt;Senior Revolving Credit Facility&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:12px;padding-top:6px;text-indent:32px;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;On February&amp;#160;3, 2011, the Company renewed, via amendment and restatement, its &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$35.0 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; senior revolving credit facility with its existing lender (the &amp;#8220;Facility&amp;#8221;), which can be increased up to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$50.0 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in the absence of any default and upon the satisfaction of certain conditions precedent specified in the Facility. The Facility expires in February 2016. Under the Facility, the Company is subject to borrowing base limitations on the amount that can be borrowed and certain customary covenants, including, under certain circumstances, covenants limiting the ability to incur additional indebtedness, make investments and acquisitions, grant liens, pay dividends, repurchase its Class&amp;#160;A common stock, close stores, and dispose of assets, without the lender&amp;#8217;s consent. The ability of the Company to borrow and request the issuance of letters of credit is subject to the requirement that the Company maintain an excess of the borrowing base over the outstanding credit extensions of the greater of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;10%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; of the aggregate amount of the Facility or &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$4.0 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;. The annual interest rate on the revolving line of credit under the Facility is (i)&amp;#160;the higher of the lender&amp;#8217;s prime rate, the Federal funds rate plus &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;0.5%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; or the one month London InterBank Offered Rate (LIBOR) plus &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;1.0%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, collectively referred to as the &amp;#8220;Base Rate&amp;#8221;, plus the applicable margin ranging from &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;0.5%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;1.0%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; or, (ii)&amp;#160;if the Company elects, either the one, two, three or six months LIBOR plus a margin ranging from &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;background-color:#ffffff;color:#000000;text-decoration:none;"&gt;1.5%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; to &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;2.0%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;. The applicable Base Rate or LIBOR margin is based on the level of average excess availability, as defined under the Facility, at the time of election, as adjusted quarterly. The Company also incurs fees on outstanding letters of credit under the Facility at an annual rate equal to the applicable LIBOR margin for standby letters of credit and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;23.0%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; of the applicable LIBOR margin for commercial letters of credit. Additionally, the Company is subject to commitment fees at an annual rate of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;0.25%&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; on the unused portion of the line of credit under the Facility.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-indent:32px;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;Borrowings under the Facility are secured by cash, cash equivalents, investments, receivables and inventory held by the Company and two of its wholly owned subsidiaries, The Wet Seal Retail, Inc. and Wet Seal Catalog, Inc., each of which may be a borrower under the Facility.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-indent:32px;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;At &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;August&amp;#160;3, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, the amount outstanding under the Facility consisted&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$2.0 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in open documentary letters of credit related to merchandise purchases and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$1.7 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; in outstanding standby letters of credit, and the Company had &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;$31.3 million&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; available under the Facility for cash advances and/or the issuance of additional letters of credit.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-bottom:12px;padding-top:12px;text-indent:32px;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;At &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;August&amp;#160;3, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, the Company was in compliance with all covenant requirements under the Facility.&lt;/font&gt;&lt;/div&gt;&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>Senior revolving credit facility.</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Senior Revolving Credit Facility</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>Senior Revolving Credit Facility</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://www.wetseal.com/role/SeniorRevolvingCreditFacility</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
