Bill De Blasio, 52, has been sworn in as New York City Mayor this morning, 1st January 2014.
He is the first Democrat since 1993 to be elected mayor of New York City.
Bill de Blasio took the oath of office administered by state attorney Eric Schneiderman outside his home a few minutes into the new year, in line with tradition.
A grander inauguration ceremony will take place later at City Hall, with former US President Bill Clinton administering the oath of office.
Mr de Blasio succeeds billionaire Michael Bloomberg, and has promised to govern with a liberal agenda.
He won November’s election by a record margin, contrasting himself with the pro-business Bloomberg years which he said had created a “tale of two cities”.
Mr de Blasio was born in Manhattan in 1961 but raised in Massachusetts by his mother’s family after his parents divorced. His father, a troubled Navy veteran, later killed himself after being diagnosed with incurable lung cancer.
His original name was Warren Wilhelm Jr. Mr de Blasio later took his mother’s maiden name.
He returned to New York to study Latin American politics at New York University and later gained a master’s degree in international affairs from Columbia University.
Mr de Blasio was joined by his wife Chirlane McCray and their two teenage children outside their home in Brooklyn for the
“To everyone, this is the beginning of a road we will travel together,” he said after he was sworn in.
He is New York’s first Democratic mayor since David Dinkins, who became the city’s first black leader in 1993.
He has promised to reverse the city’s rising income inequality and end a controversial stop-and-frisk policy which has been criticised for disproportionately targeting black and Hispanic men.
Mr de Blasio worked as an aide to Mr Dinkins when he was mayor and has also worked closely with the Clintons, managing Hillary Clinton’s successful 2000 run for the US Senate.
He was elected to New York City Council in 2001, representing his home area of Brooklyn, before becoming public advocate, the city’s official watchdog.