[7] After moving to the UK from Paris, France, in 2004, Gradel attended Lewisham College Football Academy under the tutelage of then Head Coach Aaron Jacob, who was one of his early mentors.

He attended the Bon Giourno Cup in the Netherlands, and the team went on to win the trophy, conceding no goals, with Gradel scoring 11 of 17.

On 5 May 2007, he signed his first professional contract with Leicester along with seven other players, including Eric Odhiambo, Andy King and Carl Pentney.

[9] On 6 August 2007, Leicester City manager Martin Allen made Gradel and Conrad Logan available for loan for the forthcoming season.

[25] Gradel scored his first goal for Leeds on 31 October against Yeovil Town within minutes after coming on as a substitute, which prompted chants from the crowd of "Grayson sign him up".

[citation needed] Leicester refused Leeds permission to play Gradel in their FA Cup game against Oldham Athletic.

[citation needed] Gradel scored three minutes after coming on for Leeds as a substitute in the West Yorkshire derby against Huddersfield Town.

[citation needed] He made his second league start for Leeds in the game against Brentford, due to the suspension of Robert Snodgrass.

[citation needed] Gradel replaced Jermaine Beckford as a substitute against Southampton, and he made an immediate impact in the same game; minutes after coming on, Snodgrass curled a shot into the top right corner to seal Leeds' win.

[32] Gradel handed in a transfer request on his return to Leicester,[33] and he was signed by Leeds United on a two-and-a-half-year contract on 25 January for an undisclosed fee.

[38] Gradel returned from his four match suspension in the second round of the League Cup when he made his first start of the season against his former club Leicester.

[citation needed] Gradel made his first league start of the season, when Lloyd Sam was dropped for the game against Swansea City on 11 September.

[47] Newcastle United showed an interest in Gradel but manager Simon Grayson confirmed that he wasn't looking to sell the in-form player.

[50] On 8 January, Gradel won a penalty against Arsenal which was scored by Robert Snodgrass as Leeds earned an impressive 1–1 draw.

[64][65] It was revealed on 4 August, Gradel would miss the League Cup match against Bradford City as he had been called up to the Ivorian squad.

[66] Gradel scored a late penalty in the first game of the 2011–12 season against Southampton, however it proved to be only a consolation goal as Leeds lost 3–1.

[citation needed] In the 2014–15 season, Gradel was Saint Etienne's top scorer in Ligue 1 with 17 goals, also providing three assists.

On 4 August 2015, after four years in France, Gradel returned to England to join former side and Premier League newcomers Bournemouth on a four-year deal for a reported fee of £7 million.

[73][74] As part of the deal Gradel's old club Leeds United received a percentage of the transfer fee due to a 10% sell on clause.

[75] On 29 August, Gradel tore a cruciate ligament in his knee during the match against Leicester City, with the injury ruling him out for six months.

[76] On 27 February 2016, Gradel made his return to the team, coming on as a substitute in the 21st minute for Junior Stanislas in a 0–0 draw against Watford.

[85] Gradel revealed that by moving to Leeds, he was hoping to increase his international prospects to play for the Ivory Coast national team and maybe earn a place in their 2010 FIFA World Cup squad.

[4] On 21 March 2011, Gradel received his second call-up to the squad, this time to face Benin in an Africa Cup of Nations qualifier.

[93][nb 1] On 28 December 2023, Gradel was included in the final 27-man squad for the 2023 Africa Cup of Nations hosted by Ivory Coast.