Dockery, is best known for playing the role of Lady Mary Crawley on the hit British drama.
An adaptation of Julian Barnes' 2011 Booker-prize winning novel, the movie will see Oscafr-winner Jim Broadbent in the lead role.
Rampling's recent credits include "45 Years", Mortimer starred in Martin Scorsese's movies "Hugo" and "Shutter Island" while Walter appeared in Alejandro Gonzalez Inarritu's "Babel" and Joe Wright's "Atonement", reported Variety.
The movie would be Batra's second feature after the much-lauded "The Lunchbox".
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The movie begins shooting on August 16 in London and Bristol.
Also joining the cast are Billy Howle, Freya Mavor and Joe Alwyn, who plays the lead role in Ang Lee's upcoming film "Billy Lynn's Long Halftime Walk".
The story revolves around Tony Webster (Broadbent), a divorced and retired man leading a reclusive life. He comes to know that the mother of his university girlfriend, Veronica, left in her will a diary kept by his best friend, who dated Veronica after she and Tony parted ways.
Tony revisits the past in his quest to recover the diary.