The former Villarreal and Club Brugge boss, 44, has been empowered to lead the cellar-dwellers of the Spanish top flight up the table - with Betis accruing just 10 points from their first 15 games this season.
Mel's release was announced at 9pm local time in Seville on Monday, with enraged fans rallying behind their now former boss and taking aim at the club for their poor fortunes this season.
The departing 50-year-old gave an emotional goodbye at the press conference, breaking down in tears after his farewell message to end his three-year stint.
"This is the press conference I never wanted to give," Mel said.
"I'm a professional football coach. Thanks to the president for his words.
"I have a long list of thanks…first to all the players since 2010, the medics, the kit men, (the) press.
"We've been through times that were bad, tough and together, we've got through them.
"Unfortunately, this time it wasn't possible to overcome them like this and I want to thank the Betis fans, from the bottom of my heart."
Garrido took Villarreal to fourth spot and the Champions League in his short tenure in charge of the first team in 2010-11, having spent plenty of time at the club coaching Villarreal B for three stints from 2002 to 2010.
