Duckett made his debut for Northamptonshire in the 2012 Friends Life t20 against Gloucestershire on 8 July 2012, whilst in his first year of A-Levels at Stowe School. During the 2015 season, he scored four centuries in the County Championship, just managing to break the barrier of a thousand first-class runs in the season, with 1002 at an average of 52.73. The 2016 season was one of conspicuous success for Duckett. He began the season with a new highest score of 282 not out against Sussex. He scored three other first-class hundreds during the season, scoring 185, 189 and 205, with a total of 1338 runs at 58.17 and played in the semi-final and final of the Twenty20 Blast for Northants. He finished on the winning side in the final, and had particular success in the semi-final, scoring 84 off just 47 balls, and sharing a 132 run partnership with Alex Wakely. At the end of the season, he was named as the young cricketer of the year by both the Cricket Writers' Club and the Professional Cricketers' Association. He was also named PCA Player of the Year, the first player to win both PCA awards in the same season. In March 2019, Duckett scored a double century for Nottinghamshire against Cambridge MCCU during the 2019 Marylebone Cricket Club University Matches from 168 balls. It was the fastest first-class double century by a Nottinghamshire batsman, in terms of balls faced.
Duckett was selected in the squad for the Test and ODI matches in the tour of Bangladesh. He made his England debut in the first ODI against Bangladesh. He scored 60 as England made 309 to win the game by 21 runs. He was out for a duck in the second game, which England lost. He returned to form in the final game, top scoring for England with 63 to help them chase down Bangladesh's target of 278 and win the match by four wickets to win the series 2-1. Duckett made his Test debut against Bangladesh following his good performances in the ODI side. He scored 14 in the first innings as England scored 293 in their first innings, before making 15 in the second innings as England won by 22 runs. He made seven in the first innings of the second Test, and scored his maiden Test half-century in the second innings, scoring 56, although England lost by 108 runs.
2016 India
He was also selected for the tour to India this time though batting at 4 with Haseeb Hameed opening. In the first Test between the two sides he made 13 in the first innings and did not bat in the second as the match ended in a draw. In the second Test he made five as England were dismissed for 255, and was out for a duck in the second innings as England went on to lose the match by 246 runs. He was dropped after the 2nd Test after a relatively poor series.
2017–18 Ashes tour
Duckett was deselected from the England senior team picked to face a cricket Australia XI as part the 2017-18 Ashes tour following an incident in a Perth bar. Duckett was alleged to have poured a drink over teammate James Anderson. Coach Trevor Bayliss described the incident as "trivial, but in the current climate not acceptable". The incident followed unrelated off the pitch incidents involving Ben Stokes and Jonny Bairstow. Duckett was later suspended from playing in the final three England Lions games of the tour, and issued with a fine. He was also dropped for the 2018 England Lions tour of the West Indies on account of the incident.
On 29 May 2020, Duckett was named in a 55-man group of players to begin training ahead of international fixtures starting in England following the COVID-19 pandemic. On 9 July 2020, Duckett was included in England's 24-man squad to start training behind closed doors for the ODI series against Ireland.
