Sir Kenneth will also take charge behind the camera while The Martian director Ridley Scott will co-produce.
He last appeared in and directed spy thriller Jack Ryan: Shadow Recruit.
Hercule Poirot has most famously been played on film by Peter Ustinov and, on British television, David Suchet became synonymous with the role.
Hilary Strong from Agatha Christie Productions said she was delighted with Sir Kenneth's casting.
"I cannot think of a better director or actor to bring... the character to light than Kenneth Branagh," said Ms Strong.
"We have also been delivered an amazing team of producers...  and I have no doubt that the alchemy of this extraordinary group of talented individuals and Agatha Christie's brilliant story and character will create a cinematic feast that is truly memorable."
Screen and stage star Sir Kenneth has starred in numerous films and television series, including his Oscar-nominated role in My Week With Marilyn and his long-running hit TV detective series Wallander.
His other previous film directing credits include the Oscar-nominated Henry V, in which he also starred, his comic book adaptation Thor and his live-action version of Cinderella.
He is currently co-directing and appearing on stage in Shakespeare's The Winter's Tale and in Terrence Rattigan's Harlequinade as part of the Kenneth Branagh Theatre Company season at London's Garrick Theatre.
The last, and most famous, movie version of Christie's Murder on the Orient Express was in 1974. British actor Albert Finney starred as the detective with Lauren Bacall and Ingrid Bergman co-starring.
Ustinov made three big-screen Christie mysteries, including Death on the Nile and Evil Under the Sun, but Murder on the Orient Express was not among them.
Christie's 1934 story sees the detective drawn into solving an intrigue on the famous Orient Express train travelling from Istanbul in Turkey to London.
After an American passenger using a false name is murdered while the train is stuck in a snow drift, Poirot discovers everyone on the train had some connection to the murder victim and are all therefore under suspicion.
Sir Kenneth Branagh is to play Agatha Christie's Belgian sleuth Hercule Poirot in a new film version of Murder on the Orient Express.