Club chairman John Williams said:
“These decisions are never taken lightly but always in the interests of the club.
“We are in a results business and over the back end of last season and this season to date, ours have been very disappointing.
“We would like to place on record our appreciation of Tony’s contribution and hard work during a period of transition for the club which included a change of ownership. We wish him well in his future endeavours.”
Former Baggies boss Gary Megson, who was Pulis’ assistant, will take charge of first-team affairs.