The 4-0 home defeat by Chelsea on Saturday looks to have been the final straw for the owners, who were at the Hawthorns to watch their side well beaten by the defending champions.
West Brom sit just one point and one place outside the relegation zone and with just two wins in their last 21 Premier League games - with a trip to Wembley to face Tottenham their next test.
The 59-year-old Pulis has been in charge of the Baggies since January 2015, with his assistant Gary Megson taking charge of first-team affairs until the board appoint a replacement.
In a statement, 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."