Born in Southend-on-Sea, Essex, Brokenshire studied law at the University of Exeter before beginning work with a large international law firm. Deciding on a career in politics, he stood successfully as the Conservative candidate for the parliamentary constituency of Hornchurch in the 2005 general election. When his constituency was to be abolished in the boundary changes, he sought out another constituency to represent, failing to be selected in six constituencies until being selected for Old Bexley and Sidcup. He was elected MP for the area in 2010, on a campaign devoted to preventing the closure of accident and emergency services at Queen Mary's Hospital, Sidcup, a policy on which he was unsuccessful.
Brokenshire subsequently worked as a partner at international law firm Jones Day. In this position, he advised companies, businesses, and financial institutions on company law, mergers, acquisitions, and corporate finance transactions.