LONDON — British lawmakers are scheduled on Tuesday to debate and vote on the detailed legislation for Britain’s departure from the European Union, a deal that Prime Minister Boris Johnson reached with European leaders last week.

Brexit is scheduled to take effect on Oct. 31, but Mr. Johnson has yet to receive Parliament’s support for the agreement, making the day’s events a major test of whether he has the necessary backing to make his plan a reality.

By the end of the week, if not Tuesday night, it will be clear whether Mr. Johnson has failed in his “do or die” pledge to complete the withdrawal by the end of October, even if that means leaving without a deal.

There are now just nine days until that Oct. 31 deadline, but lawmakers have blocked Mr. Johnson at nearly every turn.