Gabriel Amo, a moderate Democrat who served in the Biden and Obama administrations, won a raucous Democratic special primary election in Rhode Island’s First Congressional District on Tuesday, positioning him to become the first person of color to represent the state in Congress.

Mr. Amo, who is Black, beat out 10 other Democrats to win with about one-third of the vote in the deep-blue district with around 90 percent of the votes counted, all but ensuring that he would succeed former Representative David N. Cicilline, who stepped down in May to become the president of the Rhode Island Foundation.

He will face Gerry Leonard, a former U.S. Marine who won the Republican nomination on Tuesday, in the general election on Nov. 7 to determine who will serve out the remainder of Mr. Cicilline’s term.

The crowded primary race was a tumultuous one during an otherwise quiet political summer season, rocked by a series of scandals across the field and tensions among factions of the Democratic Party. Because of a lack of independent public polling and so many candidates dividing the vote, political observers had said it was difficult to predict how the race would go.

Aaron Regunberg, a former state legislator and progressive who won support from Senator Bernie Sanders, independent of Vermont, and Representative Alexandria Ocasio-Cortez, Democrat of New York, was widely seen as having an edge over Mr. Amo going into Tuesday’s election. He captured about a quarter of the vote.

Mr. Amo began the race with little name recognition across Rhode Island, but his campaign was buoyed by more than $600,000 in donations and support from super PACs. Mr. Amo leaned into his professional background, which includes a stint serving former Gov. Gina Raimondo, now the U.S. secretary of commerce, in the Rhode Island State House, and his upbringing in the Ocean State.

“The big reason I’m running is my story,” he said in an interview last week. “I call it a Rhode Island story.”

Mr. Amo, 35, who grew up in Pawtucket, R.I., is the son of two West African immigrants. He frequently describes his personal journey, from his days as a child chasing after the Rhode Island Public Transit Authority bus to get to school to a career in which he worked for two presidents in the Oval Office.

He made protecting Social Security and Medicare his top priorities during his campaign, in addition to tackling gun violence, bolstering abortion rights and battling climate change.