After four months of political deadlock, Lofven has the backing of the Centre, Liberals and Greens to be prime minister after a historic deal bringing together parties from the centre-left and centre-right blocs.
But he also needs the Left Party, which said on Monday it was not ready to lend its support unless Lofven gave assurances the party would still have a voice in policy-making.
Lofven said he had held constructive talks with the Left Party leader Jonas Sjostedt, but declined to say whether the party would support him in Friday's vote.
"I am ready to be nominated as Prime Minister of Sweden and to take it to a vote on Friday," he told reporters after meeting parliament's speaker.
On Monday, Lofven had said there would be no point in the speaker nominating him as prime minister unless the Left Party were prepared to back him.
September's election delivered a hung parliament and the centre-left and centre-right blocs have been at loggerheads on how to form a government without the support of the anti-immigration Sweden Democrats, a party with roots in the white-supremacist fringe and who hold the balance of power.
GRAPHIC - Election scenarios: https://tmsnrt.rs/2p45tJh (Reporting by Stockholm Newsroom; editing by Niklas Pollard and Angus MacSwan)