American defender Jonathan Tomkinson joined Norwich's Under-18s for the 2019/20 season. He had almost joined Ipswich trialling with them for six weeks in 2016 but nothing came of it. When Academy Recruitment chief Steve McGavin left Ipswich for Norwich, Tompkinson's family reached out to hin to secure a trial at Norwich. This included a spell at Colchester where they beat Spurs 3-0. He also trialled with West Brom before joining Norwich.

Before joining Norwich he had played for Solar FC and FC Dallas' Academy side in his native Texas (although his family are from East Anglia).

He was called up by the USA's Under-17s for a tournament in Holland in September 2019.

On 16th July it was announced that Jonathan had signed a professional contract until the end of the 2021/22 season.

He signed a new contract in December 2021 committing him to the club until the summer of 2024.

He was on the bench for Norwich's clash with Manchester United on 11th December 2021 following injuries to many City first teamers and his own form with the Under-23s. He was also on the bench for the following clash with Aston Villa on 14th December 2021.

He made his Norwich debut in the 2-2 draw with Birmingham in the Carabao Cup on 9th August 2022 with Tomkinson scoring an own goal on 79 minutes to give Birmingham the draw. Thankfully the Canaries won on penalties. He retained his place for the next round of the cup which finished 2-2 with Bournemouth but was lost 5-3.

Tomkinson signed a contract extension to 2025 on 12th October 2022 with Norwich retaining an option to extend the contract for a further year. He then made his league debut for Norwich against Burnley on 25th October 2022.

On 14th January 2023 he was loaned to Stevenage for the remainder of the 2022/23 season to gain regular first team experience. Stevenage boss Steve Evans said "Jonathan is a big, strong and decisive defender. By being able to play anywhere across the defence, he adds fierce competition to some already very talented players."

Although Tomkinson was limited in appearances for Stevenage, the Hertfordshire side won promotion to League One on 29th April 2023 beating Grimsby 1-0. He finished the season with 3 appearances for Norwich and 8 appearances for Stevenage.

On 6th September 2023 he completed a season long loan to Bradford City who play in League Two. In October 2023 he was called up to the United States' Under-23 team for the first time, making his debut against Mexico on 11th October 2023. He subsequently played against Japan, Iraq and Morocco. In March 2023 he was called up for the games against Guinea and France.