Bandic has run Zagreb, a city of about 800,000 people, almost continuously since 2000, and is considered one of the most influential politicians in the European Union member-state.
He was forced to resign in 2002 following a drink-driving scandal in which he fled from police, but he was re-elected in 2005.
The 61-year-old is facing corruption charges in two cases and local media has linked him to several other graft affairs.
In 2015, Bandic and 15 other people, including his closest aides, were charged with graft and abuse of power that allegedly cost the city and state budgets some three million euros ($3.4 million).
The national anti-graft bureau also charged him and two aides with illegally using 40,000 euros from Zagreb's coffers to finance a campaign gathering citizens' signatures.
In Sunday's run-off poll Bandic triumphed with 51.79 percent of the votes, results released by the electoral commission showed.
His rival Anka Mrak-Taritas, from the centre-left opposition, won 46.07 percent of the votes.
"I consider myself the hardest working Croatian," Bandic said as he visited a construction site on Monday morning.
Insisting on "working 16 hours per day, 365 days a year", he is known for populist moves such as lowering the cost of tram tickets a few months ahead of the election.
Bandic is a former official of the Social Democrats, currently the main party of opposition in the national parliament.
He was expelled from the party after deciding to run for president as an independent in 2009, a contest he lost.
The first round of Croatia's nationwide local elections were held on May 21 and seen as a test for conservative Prime Minister Andrej Plenkovic.
The ruling coalition, led by his HDZ party, collapsed in April after only six months in power.
The HDZ scored well in the local polls, winning 13 out of 20 regional governor posts and the mayoral contest in coastal Split, Croatia's second largest city.
It is still unclear whether Plenkovic will find the support of a new parliamentary majority or call a snap general election.
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
