Zelem previously played for Liverpool where she twice won the WSL in 2013 and 2014, as well as Italian side Juventus, winning Serie A in the 2017-2018 season with the club.

She then joined Manchester United, the club she came through the academy of to win the Women's Championship in their inaugural 2018-2019 season and later captained the team to an FA Cup title in 2024.

Zelem has also represented England from U15 to U23 levels, scoring 14 goals in total, prior to making her senior debut in 2021, after previously training with the squad in 2020.

[4] On 11 April 2014, Zelem suffered a broken collarbone, while on international duty for England under-19, and missed the start of the 2014 FA WSL season.

[5] After recovering from injury, she made her senior team debut on 29 June 2014, before being substituted for Nina Frausing-Pedersen in the 58th minute, in a 1–0 defeat against Arsenal in the FA WSL.

On 12 October 2014, Zelem was an unused substitute in Liverpool's win against Bristol City, as they retained the FA WSL title after a dramatic final day of the season.

[8] In November 2014, Zelem was nominated by The FA for the WSL Development Player of the Year, alongside Carla Humphrey and Natasha Baptiste.

[10] Liverpool coach Matt Beard praised Zelem, likening her to Frank Lampard and stating she has great career in the future.

[25] In the opening game of the 2018–19 Championship season, she scored her first goal for United, on her league debut, from the penalty spot in a 12–0 win away to Aston Villa.

[30] In a 1–1 draw against Reading on 2 February 2020, a penalty was awarded against Zelem after she was penalised for a handball, despite the ball hitting her head, leading to criticism of the standard of refereeing.

[40] Zelem recorded her first assist for Angel City on 12 October 2024, setting up former Manchester United teammate Christen Press' first goal since returning from a two-year ACL injury, in an 1–1 draw away against North Carolina Courage.

After draws with South Korea and Mexico, England failed to progress to the knock-out stage after being defeated by eventual finalists Nigeria 2–1 in the final group game.

[58] She began her career as a winger, developing this under the Italian style while playing for Juventus to fit more into a central role when returning to Manchester.