Ashvir Sangha was running as an independent candidate in next month's election for West Midlands Mayor, having pledged to push for a "new style, new vision and new generation in local politics".
The 32-year-old entrepreneur has now announced he has withdrawn his candidacy and backed Conservative incumbent Mr Street, who he said had the "skills, character and connections" to help the region bounce back from the pandemic.
Former Oxford Union presidents Mr Sangha said it was "clear that this is a two horse race" between Mr Street and Labour challenger Liam Byrne.
He said: "On the one hand there’s Andy – the former John Lewis boss who chose to leave business and serve as Mayor, bringing his skills, character and connections to the job.
"And on the other hand there’s Liam, a traditional politician and Labour Party lifer who in my view represents the same old politics that I’ve campaigned against.
"The future of our region is too important to be reduced to a party political football of Red vs Blue. It’s time to unite around the right candidate irrespective of historical voting habits.
"Andy is an honest, pragmatic and independent minded leader focussed on delivery. This is a rare combination in politics.
"He’s worked cross-party to champion the region. He has been different to other Mayors. He’s listened and learnt during his time in office and undoubtedly stands the best chance of securing more devolution.
"Just when we’re starting to see wins roll in for the West Midlands, let’s stick with the Mayor who helped get those wins.
"Anyone can say nice words but as voters we have to ask ourselves, who will actually get it done? It’s a close race. It’s time to withdraw and throw my support behind Andy to help tip the balance in the right direction."
Mr Street welcomed Mr Sangha’s support, saying that by pulling out he had put the interests of the region first.
The decision leaves six candidates bidding for power, with Mr Street and Mr Byrne joined by Lib Dem Jenny Wilkinson and Steve Caudwell for the Greens.
Two independents – transport campaigner Tim Weller and elections veteran Colin Rankine, who represents "biblical solutions" party Yeshua – make up the list.