Brighton released a statement to confirm Poyet's departure on Sunday night, a day before the players are due to report back for the first day of pre-season.
Poyet led Brighton to the play-offs last season but his tenure at the Amex Stadium had become uncertain after it was revealed that the Uruguayan, assistant manager Mauricio Taricco and coach Charlie Oatway were told to stay away from the club.
Brighton have remained tight-lipped over the reasons for taking the action, but Sunday's decision comes after Poyet failed to attend a disciplinary hearing last week.
"Gus Poyet has been informed today by Brighton & Hove Albion football club's internal disciplinary panel that his employment has been terminated with immediate effect," the club's statement read.
"This followed his suspension, an investigation, and a subsequent formal disciplinary process. In line with the club's own procedures, and UK employment law, Mr Poyet now has a right of appeal. As such, the club will make no further comment on this matter or recent LMA statements at this time.
"Given the close proximity of the new season, the club will, in conjunction with its board, now seek to appoint an interim manager pending the outcome of a possible appeal.
"The interim manager will oversee the initial weeks of pre-season preparation alongside the club's existing staff.
"The club's first-team players report back as planned for pre-season testing tomorrow, Monday 24th June, with the squad's first technical sessions commencing on Thursday 27th June. The team play Whitehawk on Saturday 6th July and leave for their summer training camp in Spain on 14th July."