Latvia's government has resigned after a series of corruption scandals and street protests against its policies.
Mr Kalvitis has been Latvia's longest-serving prime minister
Prime Minister Aigars Kalvitis handed in his resignation and that of his cabinet to the president, fulfilling a pledge he had made a month ago.
Recent demonstrations were triggered by the government's attempts to sack a leading anti-corruption investigator.
No successor to Mr Kalvitis has been named and few Latvians expect politics to change, a BBC correspondent reports.
Anti-government protests in Riga over the last two months have been the largest seen in the country since it gained independence from the Soviet Union.
However the parties in the current governing coalition are still in the majority. The BBC's Laura Sheeter in Riga says some, if not, all are likely to remain in power.
As a result, many Latvians will be wondering if their protests have been effective, our correspondent says.
Mr Kalvitis had announced last month that he would resign on 5 December, after several ministers quit in apparent protest over his style of leadership.
Thousands of people had also protested in the streets against his controversial attempts to sack anti-corruption chief Aleksejs Loskutovs over alleged financial irregularities.
Critics accused the prime minister of overstepping his powers and said the move was politically motivated, as Mr Loskutovs had been investigating possible campaign violations by Mr Kalvitis' People's Party.
Mr Kalvitis was eventually forced to re-instate Mr Loskutovs.
Mr Kalvitis' four-party coalition controls 56 of parliament's 100 seats.
The 41-year-old is Latvia's longest-serving prime minister, having been elected in December 2004.