A statement from the club said: “Alan has made an important contribution since joining in September 2003 but this season’s results have been disappointing.
“Chairman Eggert Magnusson and the board feel it is the right time to make a change in the club’s best interests.”
The statement continued: “The search for a successor is now underway in order that a new manager can be in place ahead of the January transfer window.
“First-team coach Kevin Keen will take temporary charge of team affairs until a new appointment has been made.
“No further statements on this matter will be made by the club before that time.”
Former Charlton boss Alan Curbishley is a favourite to succeed Pardew as West Ham manager.