During January 2016, the media linked Coventry's young midfield startlet James Maddison with £7million moves to Tottenham, Liverpool and Arsenal so it was a surprise when David McNally announced just as the transfer window closed at 11pm on Monday 1st February 2016 that Norwich had signed Maddison from Coventry on a three-and-a-half year contract for an undisclosed fee. This was reproted to be £2.5million. He was immediately loaned back to Coventry City for the remainder of the 2015/16 season. He scored once in 11 appearances on loan.

Maddison is a product of Coventry's youth team. After impressing for the club's under-18 side at the start of the 2013/14 season, Maddison was rewarded with a squad number and a place on the bench for the team's trip to Stevenage on 5th October 2013. He made his professional debut as a substitute on 13th August 2014 in a 2-1 League Cup loss to Cardiff City. He went on to make 31 appearances for the Sky Blues, scoring 4 goals, ahead of his move to Norwich.

Maddison made his Norwich debut on 23rd August 2016 in the 6-1 win over Coventry at Carrow Road in the Football League Cup. After impressing in the 6-1 win over Peterborough on 30th August 2016 in the Football League Trophy, scoring once, he was surprisingly loaned to Scottish side Aberdeen on 31st August 2016 until January 2017. "I am really excited to get James," said Aberdeen manager Derek McInnes. "James is a player with great talent and hopefully playing with us he will get a chance to showcase that. He can play in a number of positions in midfield and he is also a creative player. He is very good technically, he can make the difference in a tight game and is someone who I really hope will enjoy himself here. James is coming up to play with some very good players which he recognises. He recognises the demands of the club but all that was a big attraction for him. There were a lot of clubs interested in him because he is a good player but when we spoke to his agent and to James it was clear they seen Aberdeen as the preferred option which pleases me no end. He is here until January. We are comfortable with that and so are Norwich. We will see what transpires from there."

Maddison made 17 appearances for Aberdeen, scoring twice and playing in the final of the Scottish League Cup final (a 3-0 defeat to Celtic), before returning to Carrow Road. He made his first Championship appearance for Norwich as a substitute in the 3-1 win over Preston on 17th April 2017 with Maddison scoring Norwich's third goal. He finished the season with four appearances and one goal to his name.

Maddison's form in the first half of the 2017/18 season saw him linked with big money (£20m) moves to the likes of Liverpool, Tottenham, Crystal Palace, West Ham, Everton and Wolves. He finished the season as Norwich's player of the year, scoring 13 goals in 38 appearances. This speculation continued into the Summer 2018 transfer window with Everton, West Ham, Southampton, Fulham and Leicester being linked before he finally joined Leicester on 20th June 2018 for an undisclosed fee rumoured to be worth up to £24milion - Norwich's record sale. This is the largest ever Championship transfer deal for a player yet to feature in the top flight  In June 2021 Southampton's former vice-chairman Les Reed claimed Southampton thought they were in pole position to sign Maddison before Leicester’s financial muscle won the day. He said. “I’m still disappointed in the way we lost Maddison. “Mads was ready to sign. We had everything agreed and then there was a delay and Leicester came in and blew us out of the water.  We were not in the same league as Leicester in terms of the hikes you could make in numbers of millions on maybe a transfer fee, an agent’s fee or salary.” 

Maddison made his debut for England's Under-21s as a 81st substitute in a 2-0 win in Ukraine in a European Championship qualifier,

Maddison's impressive start to the 2018/19 season for Leicester saw him called up to the England squad at the beginning of October 2018. He had played just eight Premier League games, scoring three goals.

Maddison won his first international cap for England on 14th November 2019 coming on as a substitute in a 7-0 thrashing of Montenegro in the European Championship qualifiers. This was England's 1000th game and saw Harry Kane net a hat-trick.

Maddison came on as a 67th minute substitute for Iheanacho as Leicester won the FA Cup final beating Chelsea 1-0 at Wembley on 15th May 2021.

On 17th June 2021 the Daily Mail speculated that both Arsenal and Chelsea were interested in Maddison as they refresh their squads with Maddison seen as a replacement for Chelsea's Hakim Ziyech, who appears to be surplus to requirements under Thomas Tuchel.  Maddison is also allegedly emerging as one of their main targets to fill a problem position in Mikel Arteta’s Arsenal squad. Arteta believes the playmaker could improve his team in the final third. On 3rd August 2021 it was reported that Arsenal had bid for Maddison. Leicester have no need to sell and have priced Maddison at £60million. That figure is reportedly too high for the Gunners who have offered a player plus cash offer.

At the beginning of August 2022, Leicester rejected a £40million bid from Newcastle for Maddison which was followed by a £50m offer which was also rejected.

On Thursday 10th November 2022 he was included in Gareth Southgate's England squad for the World Cup in Qatar following Maddison's form at the start of the 2022/23 season. If Maddison starts for the Three Lions during the World Cup then Norwich would be due a significant sum as part of a clause, which was negotiated as part of the £24m deal that took Maddison to Leicester in the summer of 2018. However he didn't feature at the World Cup.

Maddison won his full international debut on 26th March 2023 as England defeated the Ukraine 2-0. This activated a clause in the contract when he moved to Leicester which meant that Norwich will receive a significant windfall for Maddison starting a competitive international.

Maddison and Leicester were relegated from the Premier League on 28th May 2023 when they lost 2-1 to West Ham on the final day of the 2022/23 season.

After weeks of speculation linking him with Newcastle and Tottenham, Maddison signed for the latter on 28th June 2023 for a fee of £40m. He had played 203 games for Leicester, scoring 55 goals and providing 41 assists. City negotiated a 15pc sell-on clause with the Foxes when Maddison moved to the East Midlands in the summer of 2018 for a fee in the region of £22million. Between 10 and 15pc of that will go to first club Coventry City, however, who retain a sell-on clause from their original £2.5million sale of Maddison to Norwich in 2016.