When votes were counted on May 16 after the marathon five-phase general election, Congress and its allies had 262 seats in parliament, compared with the BJP-led opposition alliance's 158.
Congress had campaigned on a poverty-alleviation platform for India's rural millions, steering the country through an economic downturn and ensuring growth as its main priorities. Large cabinet
The new council of ministers comprises 78 members, a mix of veteran politicians and several young faces.
Among those who were sworn in on Thursday are Farooq Abdullah, the former chief minister of Indian-administered Kashmir.
Agatha Sangma, 28, elected from the northeastern state of Meghalaya, was the youngest federal minister to be sworn in.
Shashi Tharoor, the former UN undersecretary general, was also among the new ministers sworn in.
Last Friday, Singh and a 19-member cabinet took the oath of office from Patil at a ceremony at Rashtrapati Bhavan, the presidential palace, in Delhi.
With 79 members, "this is the biggest cabinet in a decade," Paranjoy Guha Thakurta, a political analyst, said.
Singh is the first prime minister since Jawaharlal Nehru to be returned to office following a full five-year term.