SYDNEY, Australia — Australia’s divisive debate over same-sex marriage returned to Parliament on Wednesday when Prime Minister Malcolm Turnbull implored lawmakers to support a bill that would ask Australians to vote on the issue.

“If ever there is an issue to be put to a plebiscite, this is one that can be and should be because it is a very straightforward question,” Mr. Turnbull said. “We put our faith in the Australian people, and we know that their answer, whether it is yes or no, will be the right answer.”

Mr. Turnbull needs the support of Parliament to pass the bill, which calls for a plebiscite — a national, nonbinding ballot — to be held on Feb. 11. The bill, he said, would ask Australians, “Should the law be changed to allow same-sex couples to marry?”

He added, “This is a simple question.”

The speech on Wednesday was the first time Australians had heard the details of the bill, and the first time that Mr. Turnbull, the leader of the Liberal Party-led conservative coalition, had outlined his agenda on same-sex marriage since his government was re-elected on July 2.