Sancho joined Watford at the age of seven. In March 2015 at the age of 14 Sancho moved to Manchester City for an initial fee of £66,000 under the EPPP which could rise to £500,000 with add ons. Sancho continued to impress in the Manchester City academy and was one of a trio of players that the Manchester City chairman, Khaldoon Al Mubarak, said would be fast tracked into the senior set up in May 2017. In July 2017, Sancho was omitted from Manchester City's pre season tour squad due to a dispute over assurances of playing time in a new contract. It was subsequently reported that Sancho was attempting to force a move away from the club.
On 2 November 2017, Sancho was called up to the England U19 squad for the first time, joining them for 2018 UEFA European Under-19 Championship qualification matches against the Faroe Islands, Iceland and Group 8's host nation side Bulgaria. Sancho made his first start at U19 level in the 6–0 victory against the Faroes, lasting seventy minutes before being substituted for Ben Brereton; Sancho would replace Brereton on the 66th minute in the win over Iceland, which secured progression to the elite round. Sancho scored the only goal of the game against Bulgaria to help England top their group. Coming on as a substitute for Brereton, Sancho scored the last of the goals in England's 4–1 win over Hungary in the first match of the elite round on 21 March 2018.
