The Hammers went down after squandering a 2-0 lead to lose 3-2 at fellow strugglers Wigan.
And just over an hour later West Ham confirmed the club had parted company with the Israeli.
The statement read: "The club can confirm that Avram Grant is no longer the manager of West Ham United.
"First-team coach Kevin Keen will take charge of the team for the final home match of the season against Sunderland on Sunday 22 May."