Stratton, a progressive backed by Governor JB Pritzker, had trailed Krishnamoorthi in polling until recent weeks when an infusion of cash from Pritzker and hardening sentiment on immigration pushed aside the relatively moderate congressman. The race also saw competition from Representative Robin Kelly, which threatened to split the progressive vote.

The contest became contentious in its final weeks, with Krishnamoorthi and Stratton trading sharp attacks on the debate stage and in television ads over corporate money and immigration policy. Illinois Future PAC, backed by Pritzker, spent at least $11.8 million boosting Stratton and attacking Krishnamoorthi.

Krishnamoorthi had enjoyed major backing from crypto PAC Fairshake and AIPAC-aligned groups, making his defeat a notable setback for both lobbies. Stratton will face Don Tracy, a former Illinois Republican Party chair, in November and is widely favoured to win in the blue state.

If elected, Stratton would become the sixth Black woman ever to serve in the US Senate and the second from Illinois, following Carol Moseley Braun, who endorsed Stratton in the contest.

In other Illinois primary results, Daniel Biss, the mayor of Evanston, won the Democratic nomination for the Ninth Congressional District, and La Shawn K. Ford won the nomination for the Seventh District seat long held by Danny Davis.