[2] In 1983 he contested the Labour nomination to replace retiring party leader Bill Rowling in the Tasman seat, but lost to Ken Shirley.
[5] Rainbow was opposed to the Green Party's decision to join the Alliance and declined to stand for them in the seat at the 1992 Wellington Central by-election.
He served as Chairman of Auckland-based phone support and LGBT advocacy service OUTLine and also a board member of the New Zealand AIDS Foundation.
[16] In August 2024, he was appointed to be New Zealand's Chief Human Rights Commissioner from November 2024 by Justice Minister Paul Goldsmith.
[17] Left-wing blogger Martyn "Bomber" Bradbury and The Spinoff editor Madeleine Chapman criticised Rainbow's appointment, citing his alleged transphobic and pro-Israel views.
[18][19] In mid-October 2024, Chapman reported that the independent panel set up to shortlist and interview candidates for the role did not recommend Rainbow.
[20] In late January 2025, Rainbow as Chief Human Rights Commissioner condemned a "genocide hotline" established by Palestine Solidarity Network Aotearoa national chairman John Minto, stating "the promotion may not be unlawful, however, the chief commissioner sees it as potentially harmful to Israeli and Jewish people in Aotearoa New Zealand.