"New York City, I am so proud to be your 110th mayor," Adams tweeted from the NYCMayor account.
Adams was a police officer for over 20 years, retiring in the rank of a captain. He served in the New York State Senate and was then elected as the president of one of New York's boroughs, Brooklyn, twice.
Adams, who is a Democrat like previous New York mayor, Bill de Blasio, is taking over amid a spike in COVID-19 cases in the most populous city in the US.