The 52-year-old TV presenter – who quit ITV's Loose Women at the end of 2020 because she was unhappy working on the show – is filling in for Isabel Webster on Breakfast with Eamonn and Isabel and said she is prepared to "sink or swim".
Khan announced on Instagram: "Be careful what you wish for!! I’ve always wanted to be a news anchor and now I’ve got the opportunity to work with award winning broadcaster and king of news @eamonnholmes on @gbnewsonline.
"I’m covering @isabelwebstertv for just two days, Monday, Tuesday, next week - I’m absolutely nervous and feeling a bit sick just thinking about it - but doing things out of my comfort zone is good for me.
@isabelwebstertv @eamonnholmes make it look so easy - seamless from one news item to the next, flawless transitions between autocue to ad-lib and from light to shade!
"I’ll either sink or swim – but at least I can say I had ago!"
She added: "I shadowed the team last week and was super impressed with the output. Lovely morning crew, welcoming, inclusive and supportive."
Holmes, 63, commented: "Thank you for saying Yes my dear friend."
He added on Twitter: "Saying it as it is .... @sairakh and myself set up your day this Monday & Tuesday. Please tune in and expect the unexpected."
Since she quit Loose Women, Khan has been vocal about her discontent working on the panel show and said she struggled to fit in.
She also claimed the final straw came when a producer asked her to launch an account on OnlyFans as part of an 'undercover' report on the subscription-only glamour content platform.
A spokesperson for Loose Women has denied the claim.
Loose Women panelist Kelle Bryan, who has also co-hosted with Holmes wished Khan good luck, saying: "I've sat I'm your seat, you cannot get a better co host. @eamonnholmes is a complete gent and will hold your hand through it. Congratulations."
Fellows Loose Woman Andrea McLean commented: "Good luck Mrs!"
Holmes returned to the GB News show in January after four months convalescing following spinal surgery, during which time he suffered a fall at home.
Watch: Saira Khan reveals how many times she showers in a week on Loose Women