Graham Platner withdrew from the Maine Senate race on Friday, ending his tumultuous political saga and allowing Democrats to begin the process of selecting an alternate nominee.

“I write to formally withdraw my candidacy for United States Senate,” Mr. Platner wrote in a letter to the Maine secretary of state. “Please consider this notice as my official withdrawal from consideration for this office.”

Mr. Platner’s official departure from the race, which was confirmed by Jana Spaulding, an aide to the Maine secretary of state, comes two days after he announced he would suspend his campaign following an accusation of rape, which he denied. It also comes as Maine Democrats have begun conversations about how they will build a process to replace him, which is expected to culminate in a state convention in two weeks.

Maine Democrats are eyeing a late July party convention to select a new Senate nominee to replace Mr. Platner. State and county Democratic Party officials in Maine have spent this week hashing out the rules for how they will select delegates, who will then vote from among a handful of candidates already seeking the nomination.

At least six candidates have said they will enter the abbreviated contest. Three were candidates for governor who did not win that primary last month, two others lost a primary for a House seat and the other was briefly a Senate candidate before dropping his bid last year.

Mr. Platner faced a deadline of 5 p.m. on Monday to formally withdraw his candidacy. If he had not met it, he would have remained on Maine’s general election ballots in November, a potentially catastrophic development given the whirlwind of recent developments about his past.

In his departure letter, Mr. Platner recounted the successes of his primary campaign, reiterated his political platform and repeated lines from his Wednesday remarks suspending his campaign. He concluded with a vulgar remark about Immigration and Customs Enforcement and wrote “Free Palestine” and “Up the Hearts,” a reference to Portland’s professional soccer team.

Maine Democrats now have until July 27 to choose a replacement nominee. The new candidate will run against Senator Susan Collins, a Republican. The contest has long been seen as a key battleground in the fight for the Senate majority.

Tim Balk contributed reporting.