Robert White will officially take over at-large Council member Vincent Orange’s seat after the D.C. Democratic Party approved the freshman lawmaker Thursday night.

Mr. Orange decided to leave his seat, resigning from the council Aug. 15 after accepting the leadership of the D.C. Chamber of Commerce, a business group that lobbies Mr. Orange’s legislative committee.

Mr. White defeated Mr. Orange in June’s Democratic primary for the at-large seat. Because Democrats account for about 75 percent of the city’s registered voters, Mr. White is virtually assured victory in November’s general election.

Under D.C. law, the party of a resigning lawmaker can name an interim replacement. The law also says the city Board of Elections must hold a special election within 174 days of the resignation.

Mr. White, who was heavily favored to be appointed to the seat and won handily in a 43-2 vote, doesn’t have much time to get caught up. The council starts it’s fall legislative session on Tuesday.

Back in August, when rumors spread that Mr. White would likely be ordained in a landslide, he told The Washington Times that he was already studying the important legislation the council will consider in the coming months so he can hit the ground running.

Two major bills are moving through the council: One would require employers to give work schedules to employees at least three weeks in advance; the other would make businesses pay a 1 percent tax to fund paid family and medical leave for all of the District’s workers.

The D.C. Chamber of Commerce, where Mr. Orange now finds himself employed, strongly opposes both. Mr. White said he supports paid family leave and fair scheduling, though he said he is still working out the details.

“I’ve always been a supporter of paid family leave,” Mr. White said in August. “I come from a working-class family that has struggled in this city. I want to immediately pull in the paid-leave advocates and the business community to have a conversation.”