The Portugeuse had been under pressure following a poor seven-match winless streak, with sections of Owls supporters calling for his dismissal towards the end of Saturday’s 2-1 defeat to Middlesbrough.
Wednesday languish in 15th place and visit Nottingham Forest on Boxing Day. Lee Bullen will take temporary charge.
Chairman Dejphon Chansiri said: “I would like to offer my sincere thanks to Carlos for the time, effort and commitment he has given Sheffield Wednesday over the last two and a half years.
“Both parties believe the time is right to go our separate ways.
“I maintain a huge amount of respect for Carlos as a coach and as a person and he will always be welcome at Hillsborough.
“I wish him every success in the future.”
Carvalhal, who had been the longest serving manager in Yorkshire, arrived at Hillsborough in the summer of 2015 and steered the Owls to the Championship play-off final at the end of the 2015-16 season.
A second play-off campaign followed in 2016-17 but Wednesday were beaten at the semi final stage by Huddersfield.
Carvalhal said: “The chairman and myself talked after the game and we believed this was the correct timing to make this decision.
“The fans are fantastic, unbelievable, and I would like to thank them very much. They have given me some memories that I will always cherish.”