Democratic Rep. Andy Kim grabbed the New Jersey Senate seat from Republican opponent Curtis Bashaw Tuesday night, in an expected win.

The seat was vacated by former Sen. Bob Menendez, a Democrat who resigned earlier this year after being found guilty on federal bribery charges. He tried to run for reelection as an independent while facing trial but then withdrew his bid.

Mr. Kim, a three-term congressman, flipped the New Jersey district he represented in 2018, and went on to win reelection in 2020 and 2022.

Mr. Bashaw was a political newcomer running as a moderate Republican. He had a tough battle up against a more well-known name in a blue state.

Mr. Kim, 42, will become the Senate’s first Korean-American and is expected to take up the seat sooner than January because of Menendez’s resignation. Democratic Gov. Phil Murphy has said that George Helmy, who is serving the remainder of Menendez’s term, will step down and the winner of Tuesday’s election would be appointed.

• This article is based in part on wire-service reports.