In 1986, Cantwell was elected to the Washington State House of Representatives at the age of 28. In her campaign, she embarked on an extensive door-knocking effort in her district.[5] She defeated George Dahlquist 54%–46%.[6] In 1988, she won re-election to a second term with 66% of the vote.[7] In 1990, she won re-election to a third term with 61% of the vote.[8]