Writing on her official website, the star revealed that Glenda is about to find herself increasingly isolated in Walford - prompting her to leave the area behind.
Glenda first appeared on screens in January 2010 and has been at the centre of many dramas in the past year, as her schemes and secrets have caused a stir among the Mitchells.
Speaking of her EastEnders departure, Barber told her online fans: "2010 was a busy and exciting year for me playing Glenda Mitchell in EastEnders. After Glenda manages to alienate practically everyone on Albert Square, she makes her exit in March 2011.
"But will she be back in the future to wreak more havoc? Well 'she ain't dead' so anything is possible... watch this space!"
Barber added that she is currently "working on a yoga-based project with a view to bringing out a DVD later this year".
The actress's screen daughter Samantha Womack (Ronnie Branning) is also due to depart EastEnders in the months ahead.