The Championship strugglers made the announcement late on Monday night, with chairman Dejphon Chansiri indicating issues on and off the pitch were behind the decision.
Pulis's dismissal came two days after a 1-1 draw at Blackburn in his tenth game in charge.
Chansiri said in a statement on the club website: "The performances and results have not been of the level expected since Tony Pulis was appointed. There are also other issues which have had a bearing on this decision.
"On the pitch, seven points from a possible 30 is not acceptable. It is vital we maintain our Championship status and I feel I must make a change now with over half of the season remaining to give us the best possible chance of doing so."
Wednesday said first-team coach Neil Thompson would take charge of the team until a permanent replacement was found, starting with Tuesday’s game against Middlesbrough.
Former Stoke, West Brom and Middlesbrough manager Pulis was only appointed on 13 November following the departure of Garry Monk, but he won just one match, a 1-0 victory at home to Coventry on 19 December.
Wednesday lie second bottom of the table on 13 points, three points from safety.