The actress, who plays Kat Moon in the BBC soap, will leave Walford over Christmas - at the same time as on-screen husband Alfie Moon (Shane Richie).
According to a show spokesman, the decision was "mutual".
Soap bosses have declined to give any clues on her exit storyline but revealed that she will not be killed off, leaving the door open for her return. Chrissie Watts (Tracy-Ann Oberman) and Sam Mitchell (Kim Medcalf) are both set to leave at around the same time - two characters which Kat has grudges against...
Back in April, Digital Spy reported that Jessie's contract would take her to the end of the year, quashing rumours of a £100,000 'sweetener' to keep her in the show for a further six months.
Kat recently returned to Albert Square after her nan, Mo (Laila Morse) discovered her in prison while visiting a friend. The character then bid an emotional farewell when her screen daughter, Zoe (Michelle Ryan) left after confessing her involvement in Den Watts' (Leslie Grantham) grisly murder.
Jessie, however, is in talks with the BBC over projects she may undertake after her departure.
Meanwhile, producers, anxious to maintain viewing figures, are countering the major departures with the reunion of the Mitchell clan - Barbara Windsor, Steve McFadden and Ross Kemp.
A spokeswoman for the soap added: "As a newcomer we found an amazing talent in Jessie and we thank her for a fantastic contribution to the show. We wish her
all the very best for the future."
The BBC have also confirmed the departure of Charlotte Avery, who plays Johnny Allen's girlfriend Tina Stewart.