Mr Lapid, the leader of the centrist Yesh Atid party and foreign minister, will take over from Naftali Bennett under an existing power-sharing deal.
They formed an unlikely eight-party coalition after last year's election.
However it collapsed last week, clearing the way for fresh polls.
It also creates an opening for Israel's longest-serving prime minister, Benjamin Netanyahu, to return to office despite being on trial on corruption charges which he denies.
Mr Netanyahu, whose right-wing Likud party is predicted to remain the largest in the Knesset, was ousted by Mr Bennett and Mr Lapid last June, breaking two years of political stalemate.
Ahead of the vote to dissolve the Knesset, which has been delayed until Thursday morning, Mr Bennett told members of his right-wing Yamina party that he would not be standing in the upcoming election, his spokesman said. He will serve as alternate prime minister under Mr Lapid until then.