Thursday's decision came hours after House Speaker Chris Donovan withdrew as a candidate representing the minor party. Working Families had originally cross-endorsed Donovan, but Donovan lost the Aug. 14 Democratic primary to Esty.
In a written statement, Lindsay Farrell, the party's executive director, said Esty "is in the best position to fight for working and middle class families going forward."
Party co-chair Julie Kushner said the party is confident Esty "will defend Social Security and Medicare and fight to raise the minimum wage," key issues for the group.
Esty, who will now appear twice on the ballot, faces Republican Sen. Andrew Roraback. He's also been endorsed by the Independent Party.
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