Pranab Mukherjee was sworn in on Wednesday as India's 13th president in a ceremony at the country's parliament.
The position of president is largely ceremonial, but Mukherjee, a political veteran, would have a key role in determining who forms the next government in the event of a hung parliament after elections in 2014.
The 76-year-old Mukherjee is a senior figure in the Congress party who resigned his post as finance minister to run for president. He was elected last week by national and state lawmakers.
Mukherjee travelled to parliament on Wednesday in a bulletproof limousine escorted by an honour guard on horseback and in security jeeps. His arrival was greeted by the blaring of bugles.
The chief justice of India's supreme court, SH Kapadia, administered the oath of office in the flower-bedecked central hall of parliament. The prime minister, Manmohan Singh, the Congress party leader, Sonia Gandhi, and Singh's cabinet colleagues were present at the ceremony.
Soon after Mukherjee was sworn in, soldiers sounded a 21-gun salute amid loud applause from the hundreds of lawmakers who attended the event.
Mukherjee has been a Congress party stalwart since 1969 and acted as troubleshooter in managing its fractious coalitions.
At different times he has served as foreign minister, defence minister and twice as finance minister. His latest term controlling the finance portfolio from 2009 was marred by slowing economic growth, a weakened currency and rising inflation. India's annual economic growth of 5.3% in the last quarter was the slowest in nine years.