PORTSMOUTH, N.H. — Democratic voters in New Hampshire selected Molly Kelly, a former state senator, as their nominee for governor on Tuesday, as female candidates for governorships continue to show their strength in primary elections this year.

Ms. Kelly’s victory brings to 15 the number of women who have won governor’s nominations in this primary season, a record.

Backed by the local political establishment — she was endorsed by both of the state’s United States senators — Ms. Kelly, 68, defeated Steve Marchand, a former mayor of Portsmouth who ran to her left, according to results compiled by The Associated Press. She held about 65 percent of the vote with more than 90 percent of the ballots counted.

But Democrats rejected the bid of another female candidate, Maura Sullivan, a military veteran who had only moved to the state last year. She fell to Chris Pappas, a local party favorite, the A.P. reported, in a key House district that Republicans hope to target in November.