The Ecclesall representative was chosen for the leader of the opposition role by party members on Monday after Coun Colin Ross stood down.
The Lib Dems took two seats from Labour in this month’s city council elections. Coun Mohammed also stood against new Brightside and Hillsborough MP Gill Furniss in the by-election held after the death of Harry Harpham.
Coun Mohammed said: “These local elections have shown the Liberal Democrats can win again. I’m ambitious not only for the Lib Dems but ambitious for Sheffield.
“I want to represent and fight for all communities and get a fair deal for everyone in Sheffield and I’ll be taking the fight to the Labour Council who for too long have taken people for granted.”
Coun Ross added: “Shaffaq is an excellent councillor and campaigner, and demonstrated these skills leading a successful campaign as our campaign manager in the recent local elections. I have full confidence that he will be a fantastic leader and wish him all the best.”
Coun Penny Baker was voted in as deputy leader for a second term, and the Lib Dems elected their shadow cabinet of Penny Baker, Vickie Priestley, Joe Otten, Ian Auckland, Steve Ayris, Roger Davison, Martin Smith, Bob Pullin and Richard Shaw.