First-team coach and former Hibs captain David Gray will take interim charge of the team "for the foreseeable future”, assisted by Craig Samson and Eddie May.
The loss in West Lothian was the club’s seventh defeat in nine Scottish Premiership games, leaving the Easter Road side 11 points adrift of third, and eight points above the relegation zone despite a promising start to the 2021/22 campaign.
Supporters turned on Ross after the final whistle at the Tony Macaroni Arena, calling for him to be sacked, and the club confirmed on Thursday morning that Ross and right-hand man John Potter had both been relieved of their duties.
Easter Road chief executive Ben Kensell paid tribute to Ross in the wake of the club’s decision, saying: “Following the prolonged run of poor results in the league, the club has taken the tough decision to relieve Jack Ross of his duties.
“We thank Jack and John for all their hard work and dedication to the role, the club has moved forward under their leadership, and we will fondly remember some incredible highs like reaching two cup finals and finishing third in the league last season.
“We wish them all the best in their future endeavours. The club will now look to appoint a new manager to take the club and this talented young squad forward and a further update will be provided in due course.”
Former St Mirren and Sunderland boss Ross took the reins in November 2019 after spells with Alloa, St Mirren, and Sunderland. He succeeded Paul Heckingbottom and last season led Hibs to a first third-place finish in 16 years as well as taking the club to the Scottish Cup final and last four of the League Cup.
The 45-year-old departs having taken charge of 96 matches, winning exactly half of them, and had a contract running until summer 2024.
Hibs face Celtic in the Premier Sports Cup final a week on Sunday, with league matches away to St Mirren and at home to Dundee beforehand.