Campbell's teammates at Raheny United included Mary Waldron, Noelle Murray, Ciara Grant and Siobhán Killeen.

[6] In 2015 Campbell acted as a recruiter for Florida State when she approached fellow Republic of Ireland women's youth international, Megan Connolly, about playing for the Seminoles.

[13][14] Campbell had been described as a senior in Florida State Seminoles' 2014 title-winning season and had been expected to feature in the 2015 NWSL College Draft.

[20] She suffered an anterior cruciate ligament injury in November 2017 during a UEFA Women's Champions League match against LSK Kvinner FK and was ruled out for several months.

[21] In June 2020 she signed a new one-year contract with Manchester City while recovering from another long-term injury, this time to tendons in her foot.

[23] She overcame some injury-related absence in the first part of the 2021–22 season to become an important member of the title-winning Liverpool team who won promotion back to the Women's Super League.

[34] On 5 April 2014 in a 2015 FIFA Women's World Cup qualifier against Germany at Tallaght Stadium, Campbell provided two assists with throw-ins.

[4] After a two-year absence due to injuries, Campbell was called up to the senior Republic of Ireland squad again in February 2022, for the 2022 Pinatar Cup in Murcia.

[35] On 1 September 2022 Campbell started her first competitive national team match for three years in Ireland's play-off-securing 1–0 2023 FIFA Women's World Cup qualification – UEFA Group A win over Finland at Tallaght Stadium.

[37] According to her Liverpool manager Matt Beard, Campbell is an adaptable left-sided defensive player: "Meg offers a bit of versatility as she can play centre-back or left-back".