Scarlett was part of the
Tottenham Hotspur Under-18s team in the
2019–20 season; however, the season ended prematurely for him after he sustained a knee injury. He started playing with the first team in pre-season friendly matches in August 2020 and returned to the Under-18s at the start of the
2020–21 season. He scored ten goals and made three assists in eight games; He first appeared on the first-team bench at
White Hart Lane in a
UEFA Europa League game against
Ludogorets Razgrad on 26 November, and he made his debut after coming on as a substitute for
Lucas Moura. At the age of 16 years and 247 days, this made him the youngest player to have appeared in a senior first-team competitive game for Tottenham, beating the previous record held by
John Bostock. The
record lasted until 10 January 2021 when
Alfie Devine made his debut at the age of 16 years and 163 days. On 12 January 2021, Scarlett scored five goals for the Under-18 team in a 6–2 win over
Newport County in the
FA Youth Cup. He made his
Premier League debut on 7 February 2021, coming off the bench during stoppage time against
West Bromwich Albion. Manager
José Mourinho said, "
I wanted to be the one to put him on in a Premier League match. Because I know that he will be somebody in a few years." On 24 February, he became the youngest player to make an assist in the Europa League since
Kylian Mbappé in a 4–0 win against
Wolfsberger AC, teeing up
Carlos Vinícius for the goal. On 28 March 2021, Scarlett signed his first professional contract with Tottenham Hotspur. Having enjoyed a promising pre-season, Scarlett was seen as having "big, big expectations" by new manager
Nuno Espírito Santo. Scarlett made his first start for Spurs on 19 August 2021 in the inaugural
UEFA Europa Conference League competition, playing in a 1–0 defeat to
Paços de Ferreira. New manager
Antonio Conte said that Scarlett was "the best prospect from the academy" in February 2022. The following month, Conte urged the player to show patience with his lack of game time as he had noticed that he was "improving a lot". He played seven first-team games for Spurs during the
2021–22 season, On 27 July 2022, Scarlett was loaned to
League One side
Portsmouth for the
2022–23 season. He scored his first professional goal in a 1–0 win at
Port Vale on 27 August. On 3 September, he scored both Pompey's goals in a 2–1 win over
Peterborough United at
Fratton Park to conclude a run of four goals in three games. Manager
Danny Cowley said that he was the best defensive forward he had seen in 15 years. Cowley was sacked on 2 January. His successor,
John Mousinho, later admitted that Scarlett "struggled to get a place" in the
first XI, however, showing "how competitive it is in league football". Interim manager
Simon Bassey mused that "
sometimes, failure is good... I am sure Dane is going to be a good player". Scarlett ended the campaign with six goals in 40 appearances. Spurs interim manager
Ryan Mason said that he had returned as a physically stronger player. On 31 August 2023, Scarlett signed a new contract with Tottenham to run until 2027 and joined
Championship side
Ipswich Town on loan until the end of the
2023–24 season. He made 12 substitute appearances for the Tractor Boys, He returned to the Spurs team for their third round
FA Cup game against
Burnley, coming on in the 83rd-minute as a substitute for
Richarlison. On 12 August 2024, he returned to the Championship on a season-long loan at
Oxford United. He scored his first goal for the U's, an injury-time equaliser, against
West Bromwich Albion on 19 October. He struggled for playing time under manager
Des Buckingham due to the form of
Mark Harris. He featured even less, however, after
Gary Rowett replaced Buckingham as manager and signed both
Ole Romeny and
Tom Bradshaw in the January transfer window. Scarlett was recalled from his loan by Tottenham on 20 January, having scored four goals in 22 games for Oxford. He played five games for Spurs in the
2024–25 campaign, Scarlett made five substitute appearances for Tottenham during the
2025–26 season, before he was loaned to
Scottish Premiership club
Hibernian on 30 January. ==International career==