In January 2018, Wishart drew media attention for holding up a placard which read "nul points" in the House of Commons, after having asked Prime Minister Theresa May how she would rate her government's handling of Brexit from one to ten. After May had answered, Wishart received a warning by Speaker of the House John Bercow for the stunt.
In February 2018, he warned that the SNP risked alienating Scottish voters who had voted "Leave" in the 2016 referendum on European Union membership. In an article for The National, he wrote that his party had to "face up" to the reality that Scotland would be leaving the European Union, and made the case for an alternative vision of Scottish independence which involved a "graduated" re-entry to the European Union from "EEA, then EFTA then full EU membership", stressing that the final step of rejoining the EU should only be done with the "full consent of an independent Scottish Parliament". Later in February, he ruled himself out of the 2018 Scottish Depute Leadership election following the resignation of Angus Robertson. Wishart concluded that he did not have "sufficient support" to run for the Depute Leadership of the Scottish National Party.