Born in Prestwich, McManus started her professional career with Manchester City Women, making over a century of appearances for them in all competitions over two spells at the club.
In 2013, she spent one season at Sheffield FC Ladies, featuring for them 13 times, as the South Yorkshire side went on to win the FA Women’s Premier League North Division title, before returning to Manchester City Women the following campaign.
Her WSL debut came in May 2014 against Everton and scored her first goal for the club against Liverpool during the 2014 WSL Cup, which Manchester City went on to win after beating Arsenal in the final.
McManus lifted the Women’s Super League title with Manchester City for the first time in the club’s history in 2016, and has won the Women’s FA Cup twice and the WSL Cup a further two times.
The centre-back also played in a UEFA Women’s Champions League Semi-Final for the Citizens.
In May 2019, McManus signed for Manchester United. She made 16 appearances for them in all competitions, before heading out on loan to Tottenham Hotspur for the remainder of the 2020/21 season.
She has represented England Women 17 times, featuring for them at the FIFA Women’s World Cup in 2019, when they placed fourth.
McManus was made joint vice-captain upon her arrival at LCFC Women and scored the Club's first home goal in the WSL, during a defeat to Manchester United at King Power Stadium in September 2021.