BBC – The centre-right Mr Macri took the oath of office in Congress but his inauguration was boycotted by his predecessor, Cristina Fernandez de Kirchner, in a row over the venue.
In his inaugural speech, Mr Macri vowed to tackle corruption, poverty and drug trafficking.
He also pledged “team work” and an end to confrontation in politics.
Mr Macri, 56, told Congress: “As president I want to be a citizen who can communicate with all Argentines.
“Politics for me is not a competition to see who’s got the bigger ego. It’s working together for the good of the people.