His decision follows a call on Wednesday by Labour's national heritage spokeswoman, Ann Clwyd, for a review of Granada's north-west England ITV franchise because of 'boardroom savagery' that was 'making life impossible for those capable of producing high-quality television'.
Mr Fitzwalter, a passionate advocate of investigative television journalism, was associated most strongly with the prime-time current affairs programme World in Action, as editor from 1976 and executive producer from 1986.
He is known to have been unhappy since December when Dianne Nelmes, who had worked for him as editor of the programme, was promoted above him in the hierarchy as head of all Granada's factual programmes.
Mr Fitzwalter is the latest in a series of key Granada people to have quit in the year since David Plowright was forced out as managing director by Gerry Robinson, chief executive of Granada Group. Mr Plowright's successor, his former deputy Andrew Quinn, left after a few months to run the ITV network centre. Their departure was seen as weakening senior management's commitment to serious journalism.
In her complaint to the ITC, Ms Clwyd pointed out that only two of the 13 directors in place when Granada put in its bid for franchise renewal remained in post.