She'll play Sandy Gibson and her surprise arrival in Walford will air this autumn.
But it’s not quite the reunion with her daughter, Dotty, that Sandy was hoping for as she can't escape her troubled life.
Her past alcohol problems led Sandy to a fleeting relationship with the notorious Nick Cotton in which she fell pregnant with Dotty, but she originally kept her pregnancy a secret.
She eventually told Nick about their daughter whilst he was in prison and he took over custody upon his release, lying to Dotty that Sandy had passed away in a car accident.
Sandy was last seen on the Square in 2010 when Dot was instrumental in reuniting mother and daughter against the wishes of her son and since Dotty returned to Walford in 2019, Sandy has stayed well away.
No one is more shocked than Dotty when her mum drops by unannounced and causes chaos in the process.
Speaking about her arrival to Albert Square, Martha said "I have watched EastEnders since it began and I’m beyond excited to join such an iconic show and having a great time playing Sandy."
Executive Producer for EastEnders, Jon Sen added "Martha is a brilliant addition to our cast – we’re excited to welcome her to Walford. To say Sandy has a chequered past is an understatement and it’s no secret that Dotty’s upbringing was marred by her parents. Sandy’s arrival catches Dotty off guard and she’ll be forced to confront everything she’s tried to leave behind."
Martha Cope has appeared in many popular television shows including Doctors, Men Behaving Badly, Family Affairs, Doctor Who, and Holby City.
EastEnders continues Mondays, Tuesdays, Thursdays and Fridays on BBC One