Sancho joined Watford at the age of seven. Due to issues with commuting across London to the club's academy, he moved into accommodation provided by Watford and began attending their partner school Harefield Academy as a boarder, aged 11. At the age of 14 he told his Watford under-15s coach about his intention to play for England.

At the age of 14, he moved to Manchester City in March 2015 for an initial fee of £66,000 under the Elite Player Performance Plan, potentially rising to £500,000 with add ons. Sancho continued to impress in the City academy and was one of a trio of players that City chairman, Khaldoon Al Mubarak, said would be fast tracked into the senior set up in May 2017. In July, Sancho was omitted from 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 engineer a move away from the club and City were alarmed at Sancho's attitude after he missed training following a pre-season tour.
Sancho signed for German Bundesliga club Borussia Dortmund on 31 August 2017 for a fee reported to be in the region of £8 million and was immediately included in the first-team squad. He later stated that he felt confident in making the move abroad due to his previous experiences in relocating with Watford and Manchester City. Sancho made his debut for the club against Eintracht Frankfurt on 21 October, coming on as a substitute with six minutes left of the match, becoming the first Englishman to play a Bundesliga match for Dortmund. Sancho made his first league start for Dortmund on 14 January 2018, hitting the woodwork in a goalless draw with VfL Wolfsburg. He scored his first professional goal on 21 April. It was the first goal in a 4–0 victory against Bayer Leverkusen in the Bundesliga and he also assisted two other goals in the same match.

Having signed a new contract keeping him at the club until 2022, Sancho enjoyed a successful October 2018 by being named Bundesliga Player of the Month, registering three goals and an assist in just three league games. Included among his goals for the month was a brace in a draw against Hertha BSC which saw him become the first player born in the 2000s to score twice in a single Bundesliga match and the youngest ever by a Dortmund player. On 24 October, he also became the first player born in the 2000s to score in the UEFA Champions League for Dortmund against Atlético Madrid.

During a 3–3 draw with TSG Hoffenheim on 9 February 2019, he became the youngest-ever player to score eight goals in a single Bundesliga season, breaking the record previously held by Christian Wück. Later that month, upon scoring in a 3–2 win over Bayer Leverkusen, he broke Lukas Podolski's record to become the youngest player to score nine Bundesliga goals, …

Read more on Wikipedia

Sancho was capped by England's youth teams at under-16, under-17 and under-19 levels.

In May 2017, Sancho was part of the England under-17 team that reached the final of the UEFA European Under-17 Championship, and was named player of the tournament for his performances. In September 2017, Sancho was named in England's squad for the 2017 FIFA U-17 World Cup but the player's new German club resisted the call up. The two parties eventually reached an agreement where he would be available for the group stages of the competition, but his participation was not guaranteed if England progressed to the knock out rounds. On 8 October 2017, he scored twice in England U17's first match, against Chile. On 16 October, during England's round of 16 tie against Japan, he was withdrawn from the competition by Borussia Dortmund.

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 team Bulgaria. He made his first start at U19 level in the 6–0 victory against the Faroes, lasting seventy minutes before being substituted for Ben Brereton; He replaced Brereton in the 66th minute in the win over Iceland, which secured progression to the elite round. He scored the only goal of the match 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.
Following an impressive start to the 2018–19 season, Sancho was called up to the England senior squad for the first time on 4 October 2018 in preparation for UEFA Nations League fixtures against Croatia and Spain. He made his debut as a 78th-minute substitute against Croatia on 12 October, in a 0–0 away draw. On 22 March 2019, Sancho started his first competitive match for England in their 5–0 win over the Czech Republic at Wembley Stadium for a UEFA Euro 2020 qualifying match. During the September internationals, Sancho scored his debut goals for the senior team, a brace, in a 5–3 home victory over Kosovo in a Euro 2020 qualifier on 10 September.

On 11 July 2021, Sancho was brought on as a 120th-minute substitute for Kyle Walker during the UEFA Euro 2020 final against Italy. He took England's fourth penalty in the subsequent shoot-out, which was saved by Gianluigi Donnarumma. Following the 3–2 loss on penalties, Sancho along with Marcus Rashford and Bukayo Saka (who also missed penalties) were subjected to racially abusive messages on social media.

Sancho was not included in England's squad for the 2022 FIFA World Cup or UEFA Euro 2024.

Regarded as a quick, highly technical, and creative player, with excellent dribbling skills and ball control, Sancho is known for his trickery and use of feints in one-on-one situations and was described as one of the world's best young players during his Dortmund days. Although he is known in particular for his ability to get past opponents and create chances for teammates, he is also capable of scoring goals himself.

Sancho featured as a second striker or wide midfielder typically in a Borussia Dortmund 4–2–3–1 formation on either wing of attack. Dortmund's "young player project" helped Sancho function in the focal point of attack alongside a core of talented young stars like Erling Haaland, Gio Reyna and Jude Bellingham.