The region's Mayor said Ms Truss had given her "full support" to plans for a gigafactory, the Midlands Rail Hub and the Metro, decarbonisation and the trailblazer devolution deal.
Meanwhile Rishi Sunak had failed to give him "firm commitments" and would struggle to win support at an election due to his role in Boris Johnson's resignation, Mr Street said.
The Mayor also said Ms Truss had already shown she was a friend to the West Midlands, having played a key role in signing off on the region's housing deal and in encouraging Birmingham to go for the Commonwealth Games.
Mr Street's support for Ms Truss is considered a major intervention in the race for Number 10, and comes after she was also backed by former leadership contender Penny Mordaunt.
He told the Express & Star the Foreign Secretary had pledged to back manufacturing and had "committed the full weight of the government" behind winning private sector investment for a gigafactory in Coventry.
She was also committed to levelling up and had made "substantial steps forward" by backing the Midland Rail Hub, he said, as well as 'investment zones' that can leverage funding for projects such as the Metro.
"We got down to some really specific conversations about what a Liz Truss government would do for the West Midlands," Mr Street said.
"She has reaffirmed the West Midlands Combined Authority (WMCA) will continue to be a trailblazer for the devolution deal, which is absolutely critical, and has committed to support around decarbonisation.
"She has given her full support, which has satisfied me that she would respond to the things we have asked for positively."
Asked why he had chosen Ms Truss over Mr Sunak, the Mayor said: "Quite simply Liz has convinced me more. It has proven difficult to get the firm commitments from Rishi Sunak that I believe Liz Truss will bring about.
"I also believe Liz will win for my party. She has a good record in government and is likely to be able to connect with people due to her very robust and principled approach."
Mr Street also suggested Ms Truss would benefit at the ballot box having stayed loyal to Mr Johnson after others had moved to force him out.
He said: "Liz was loyal to the Prime Minister and laid out her stall for leadership after he had resigned.
"As a result she was untouched by some of the criticisms that followed, and it has to be acknowledged that Rishi is not in the same position.
"She's able to draw a line under what's happened and as a new leader, people will judge her on her merits. That would be much more difficult for Rishi to do."
According to Mr Street, Ms Truss has already proved her commitment to the West Midlands during her time as Chief Secretary to the Treasury.
He said she had signed off on investment including the region's landmark housing deal and the Edgbaston Metro extension. "She also signed the letter to Birmingham Council which gave them confidence to do the Commonwealth Games," he added.
"There is clear evidence that she has worked with us in the past. Her time in the Treasury was a good time for the West Midlands."