Before playing Poirot, David Suchet played Chief Inspector Japp opposite Peter Ustinov as Hercule Poirot in Le couteau sur la nuque (1985). Suchet considers his performance as Japp to be the worst performance of his career, while he considers Poirot to be his best.
To simulate the overweight physique of Hercule Poirot, David Suchet, who is much slimmer, wore body padding. He also wore wing collars to make his neck appear fatter.
In preparation for the role, Sir David Suchet read every book and short story in which Poirot appeared: "I had my file on one side of me and a pile of stories on the other side and day after day, week after week, I ploughed through most of Agatha Christie's novels about Hercule Poirot and wrote down characteristics until I had a file full of documentation of the character. And then it was my business not only to know what he was like, but to gradually become him."
Sir David Suchet stayed in character as Poirot at all times when on set, whether the cameras were rolling or not.
Several days before filming, Sir David Suchet would often dress up and act as Hercule Poirot. He would immerse himself in the role by acting like the detective even with his own family at home. This made his transition to the role easier when filming started.