In July 2015, Tice co-founded, with the businessman Arron Banks, the pro-Brexit Leave.EU campaign group. It was originally known as The Know.EU before being rebranded in September of that year as Leave.EU. He also donated £38,000 to the pro-Brexit campaign group Grassroots Out. Shortly after the United Kingdom voted to leave the European Union in the June 2016 referendum, he left Leave.EU, and co-founded the pressure group Leave Means Leave. He co-chairs it with the businessman John Longworth. In October 2017, they were placed jointly at Number 90 on Iain Dale's list of the "Top 100 Most Influential People on the Right".