The decision was taken in the wake of Saturday's 5-0 home drubbing by Real Madrid which left Betis five points adrift at the foot of the table.
They have won just two games all season, although Garrido is not entirely at fault, with Pepe Mel, now at West Brom, having been in the chair before him.
The 44-year-old leaves without winning a single Primera Division match, though, while his two victories, in the Copa Del Rey, mattered little as his men were beaten by Bilbao in the second leg of their tie this week.
Betis announced the decision on their website, saying they had a man lined up to take over.
"Juan Carlos Garrido is no longer the coach of Real Betis," read a statement.
"The club has decided to dispense with his services. The coach, who has not achieved the desired results, will not lead the team tomorrow. The intention of the board is that the new coach, who arrives tonight, will immediately take over the team.
"The club wishes to acknowledge the work and dedication of Juan Carlos Garrido and his staff during these months and wishes him luck for the future."
The club later confirmed former Argentina international Gabriel Calderon had been named coach until the end of the season.
Calderon, 53, is a former Betis midfielder having played for the club between 1983 and 1987. He also had spells at Independiente and Paris St Germain
Since ending his playing days in 1994 Calderon has managed extensively in the Middle East and famously led Saudi Arabia to qualification for the 2006 World Cup. Most recently he was head coach of the Bahrain national team.
Speaking on Betis' website, Calderon said leading the club was "the dream that I always had".
He added: "I come with the hope and the belief that we will move forward."