Mr Street said the Foreign Secretary offered a "bold, optimistic vision for the country" and would "deliver for the people of the West Midlands".
He gave four reasons for backing Ms Truss ahead of former Chancellor Rishi Sunak, having spoken with both candidates before making his decision.
Mr Street said Ms Truss's 'plan for growth' – focusing on new hi-tech sectors – would address the cost of living crisis by supporting the Midlands' advanced manufacturing industries and helping to attract "massive" levels of private investment.
He said Ms Truss was committed to levelling up, and would deliver on Tory manifesto pledges such as accelerating devolution to regions including the West Midlands.
She would "do what it takes to seize the opportunities zet zero offers", he added, while also lead in a "values driven way whilst guaranteeing our nation's stature in the world".
Mr Street said: "As she has shown while facing down Vladimir Putin, Liz Truss is not afraid to stand up for our values.
"As Prime Minister she will continue in that vein, ensure standards in public life, and battle for the values that have made Britain a modern, inclusive society.
"For those reasons, I shall be supporting Liz Truss for leader and our next prime minister.
"I believe she offers a bold, optimistic vision for the country. I believe she has the plan to get our economy growing again.
"And I believe she has the grip needed to get the Government firing on all cylinders to protect people’s livelihoods.
"I look forward to working with her to deliver for the people of the West Midlands."
Mr Street's endorsement comes in the week ballot papers are being sent out to Tory members, who will elect the next party leader in September.
The region's Tory MPs are split over the two candidates.
The majority are backing Ms Truss, who is considered the overwhelming favourite among members and has supporters including Aldridge-Brownhills MP Wendy Morton, Stone MP Sir Bill Cash, Dudley North MP Marco Longhi and Lichfield MP Michael Fabricant.
Meanwhile South Staffordshire MP Sir Gavin Williamson, Dudley South MP Mike Wood and Halesowen & Rowley Regis MP James Morris are all publicly supporting Mr Sunak.
Mr Wood and Mr Morris have been on the end of a backlash after pledging their support for "Judas" Rishi Sunak in the Tory leadership election.
Mr Street initially supported Jeremy Hunt, who was bombed out of the contest in the first round of parliamentary voting.