Braithwaite ran for the Liberals in the 1963 provincial election, and defeated Progressive Conservative candidate Geoffrey Grossmith to win the newly created constituency of Etobicoke by 443 votes. The original declared result showed Grossmith winning by over 500 votes, and Braithwaite was only declared elected after a serious error in the vote totals was discovered by his campaign team. The Returning Officer claimed it was an accident, due to pre-count tests of the mechanical adding machines that were not cleared before the official count began.