Macri, the former mayor of Buenos Aires who hails from one of Argentina's richest families, took the oath of office in Congress in front of legislators, several Latin American heads of state and other dignitaries, including former Spanish King Juan Carlos I.
"Today a dream is being achieved," said Macri as he took the oath 15 minutes ahead of schedule, surprising commentators who noted Argentina isn't known for such punctuality.
Macri said the nation of 41 million people was entering the 21st century behind in its development, and that its education system needed modernised at all levels.
He said that "lying about and hiding" the state of the economy had tarnished Argentina's reputation worldwide, a clear dig at the Fernandez administration, which often put out suspect figures on inflation, poverty rates and GDP.
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The 56-year-old ran on promises to usher in an era of more civil discourse and roll back much of the Fernandez administration spending that many economists say has brought Argentina to the brink of another financial crisis.
Throughout his campaign, Macri argued that measured free-market reforms would overhaul the struggling economy. He also promised to be a leader "who listens more and talks less," a clear contrast with Fernandez, who frequently blasted opponents during hours-long speeches.
Fernandez, and before her late husband and predecessor, Nestor Kirchner, dominated Argentina's political landscape for the last 12 years. The power couple sharply increased spending on social welfare programs while raising tariffs in attempts to protect local industries and aligning the country with leftist leaders like late Venezuelan President Hugo Chavez and Bolivian President Evo Morales.
Macri has promised to undo many of those policies and improve relations with the United States.