Stewart supported remain in the 2016 referendum on the UK's continued membership of the European Union. Following the result of the referendum, he tried to argue for what he called a "sensible, moderate deal" that could act as a compromise between Remain and Leave voters. He argued that although the referendum made it necessary to leave the EU, Britain should seek "to stay very close to Europe diplomatically and politically and economically". He was initially a prominent advocate for Brexit withdrawal agreement negotiated by the prime minister Theresa May, arguing that the agreement respects the result of the referendum "by leaving EU political institutions...and by taking back control over immigration" while also addressing "the concerns of the more than 16 million who voted remain" and protecting the British economy.