On 31st January 2020, Norwich coimpleted the signing of Coventry City full-back Sam McCallum for an undisclosed fee (rumoured to be around £3million). He was then loaned back to Coventry for the remainder of the 2019/20 season.

Born in Canterbury, McCallum began his playing career with non-league Herne Bay. He was also capped by England Schools' Under-18s. After a period with Jamie Vardy's V9 Academy, he signed for Coventry in Augiust 2018. He made his first team debut in the EFL Trophy in November 2018 against Cheltenham before a full league debut in December 2018 against Southend United. He went on to make 35 appearances, scoring three goals. It was reported that Liverpool and Leicester were also interested in signing him.

Coventry manager Mark Robins said: "Sam is a player with great ability and potential in the game, and there has been much interest in him this season. To us, it was unfortunately a case of ‘when’ not ‘if’ Sam would leave, such was the level and nature of the interest. We rejected an offer earlier this week for him, but Norwich have now made a substantial bid that we have accepted. As part of the deal, Sam will return on loan to us for the rest of the season and we look forward to continuing to work with him and have no doubt he will be an important and positive influence in the rest of the campaign.”

On 9th June 2020, clubs in Leagues One and Two voted to end the season due to the Coronavirus pandemic and calculate final placings based on points per game. This meant that Coventry returned to the Championship as Champions

Sam made his competitive first team debut for Norwich in the Carabao (League) Cup first round clash at Luton on 5th September 2020 which Norwich lost 3-1. The Canaries had 15 first teamers missing due to international call-ups with a further two injured.

On 20th September 2020 Sam returned to Coventry joining them on a season-long loan. He made 41 Championship appearances, the majority of which were starts as a left wing-back, and contributed a goal and two assists, helping the Sky Blues to a final position of 16th and 12 points clear of the relegation zone.

On 12th July 2021 McCallum joined QPR on a season-long loan. QPR boss Mark Warburton said "He brings real ability and will add competition to the squad. He also understands the wingback role, he has an attacking instinct, great physicality and is aerially very strong as well.Sam is a player who can have an impact in both boxes, and I am looking forward to working with him."

He made 10 appearances for QPR scoring twice.

He made 25 appearances for Norwich during the 2022/23 season.

Sam scored his first goal for Norwich on 23rd December 2023, coming on as half-time substitute against Huddersfield at Carrow Road and scoring two minutes later in what would finish as a 2-0 home win for Norwich.

In a Pink Un article on 19th May 2024, it was reported that City would not retain McCallum on the expiry of his conract and that Stoke were interested in signing him. Sam had played 34 games in 2023/24, scoring once to take his total to 60 appearances. It was confirmed the following day that McCallum would be leaving Norwich.

On 25th June 2026 it was reported by The Sun's Alan Nixon that Sheffield United were keen on signing McCallum. United’s transfer dealings are delicatewith a pending takeover leaving things in flux. But Nixon claims that McCallum could be an exception as he wouldn’t incur a transfer fee. He finally signed for the Blades on 11th July 2024, signing a four year deal.