The embattled Marino announced earlier this month he was to step down, only to withdraw his resignation on Thursday -- despite his own party calling on him to go.
But Friday's move by a majority of the Italian capital's councillors -- 26 out of a total of 48 -- automatically unseats the mayor and ushers in a temporary commissioner to run the city while new elections are organised, possibly next year.
Former surgeon Marino is one of the most unpopular politicians in Italy, facing mounting public anger over litter-strewn and pot-holed streets, a failing public transport system and revelations of Mafia infiltration of the municipal authority.
The 19 councillors from the Democratic Party (PD), which Marino represents, on Thursday had reportedly threatened to collectively resign if he stayed in post, and gained the support of seven others to trigger his ousting.
Marino has faced intense scrutiny over restaurant bills settled with a city hall credit card, in a case dubbed "Dinnergate".
He said all the money had been spent legitimately on official entertainment but that he would cover the cost as a personal gift to the cash-strapped capital.
Marino was elected with a strong reputation for personal honesty, but his administration has been buffeted by a series of damaging stories since he began his five-year term in 2013.
Earlier on Friday Marino defended himself, saying he was "certain of never having used public money for private purposes."