The 68-year-old - who was awarded an OBE in 2000 - will play Harvey Freeman, a mysterious 60-something freelance journalist who is tasked with reporting on the local elections for the Walford Gazette.
Described as a chancer and a ladies' man, Harvey first appears in Albert Square in May as best friends Pat and Peggy decide to run against each other for councillor.
Following her decision to pull out of the running last year, Queen Vic landlady Peggy - played by matriarch Barbara Windsor - enlists herself as this year's candidate. However, Peggy is seething when Pat (Pam St Clement) also decides to stand.
With their friendship put to the test, their local election battle is further heightened by Harvey's presence on the Square during the campaign period.
Both Pat and Peggy have their eyes on "perfect gent" Harvey, but the situation soon makes them realise that their friendship is worth more than what he has to offer.
Speaking of his casting, Jarvis said: "I'm absolutely thrilled to be a potential thorn between two roses working with two actresses I greatly admire and have had the pleasure of working with before. I'm delighted to be reunited with Pam and Barbara and to have a part in EastEnders."
Outgoing executive producer Diederick Santer added: "I'm delighted that the wonderful and charming Martin Jarvis will be joining us in Walford, and I can't wait to see his scenes with Barbara and Pam."
Jarvis's acting credits include Titanic, Doctor Who, Murder She Wrote, A Touch of Frost and US show Numb3rs.