The Glasgow MSP has secured the endorsement of 66 councillors across the country as he bids to lead the party north of the Border. They include Edinburgh council deputy leader Cammy Day and former Scottish Government sports minister Frank McAveety.
He will face competition for the vacant role from left-winger Monica Lennon, with a new leader to be announced by the party on February 27.
Mr Sarwar said: “More than ever, our country needs political leadership that will bring people together.
“The next parliament must be a Covid Recovery Parliament that prioritises people’s jobs and our NHS, so that we never again have to choose between treating a virus or treating cancer.
“Our opponents want to take us back to old divisive politics, which is why we need to rebuild Scottish Labour and then work to rebuild Scotland.
“Our local councils will be at the forefront of that recovery, but they have been starved of funding for years by the SNP. It’s time for a fair deal for local authorities."
In a joint letter, 66 Scottish Labour councillors wrote the Glasgow MSP is the "candidate best placed to help rebuild the Scottish Labour Party, to transform us into a credible opposition and a party that is fit for the future”.
Other signatories to the letter include former Dunfermline FC manager Jim Leishman, now a councillor in Fife, former MSPs Hanzala Malik and Elaine Murray, as well as senior Edinburgh councillor Scott Arthur.
The letter states: "Anas will create a strong opposition to hold both governments to account. And he has the positive ambition for an alternative vision to rebuild Scottish Labour and rebuild Scotland, ensuring the next five years are fully focused on the real challenges facing our country through a Covid Recovery Parliament.
“As local councillors who represent diverse areas across Scotland, we know that he is committed to strengthening Scottish Labour’s position in local government. We welcome his commitment to bringing our movement together and believe he should be the next leader of the Scottish Labour Party.”
Scottish Labour members and affiliated supporters will be able to cast their votes from February 9 until ballots close on February 26.
Ms Lennon, currently the party's health spokeswoman, announced her candidacy for the leadership on Sunday.
"Following discussions with party members, I have decided to put my name forward to lead the Scottish Labour Party," she said.
"Our members deserve to have their say about the best way to take forward our vision for a fairer and more equal Scotland. I look forward to being considered."
The contest is taking place just a few months ahead of the Scottish Parliament election, which is scheduled to be held on May 6.
Mr Leonard announced last week that he would be standing down because of continuing speculation about his leadership of the party north of the Border.