Mr Li, the son of an official in Anhui, is a fluent English speaker
China's leaders have named Li Keqiang premier, placing him at the helm of the world's second-largest economy.
Mr Li, who already holds the number two spot in the Communist Party, takes over from Wen Jiabao.
Mr Li was elected for a five-year term but, like his predecessor, would be expected to spend a decade in office.
On Thursday, Xi Jinping was confirmed by legislators as the new president, completing the transition of power from Hu Jintao.
Li Keqiang's widely-signalled elevation was confirmed by 3,000 legislators at the National People's Congress, the annual parliament session, in Beijing. He received 2,940 votes to three, with six abstentions.
As premier, he will oversee a large portfolio of domestic affairs, managing economic challenges, environmental woes and China's urbanisation drive.
The appointments seal the shift from one generation of leaders to the next. A raft of vice-premiers and state councillors will be named on Saturday, before the NPC closes on Sunday.
Mr Li, 57, who is seen as close to outgoing leader Hu Jintao, speaks fluent English and has a PhD in economics.
He has called for a more streamlined government, eliminating some ministries while boosting the size of others.
The son of a local official in Anhui province, he became China's youngest provincial governor when he was tasked to run Henan.
But his time there was marked by a scandal involving the spread of HIV through contaminated blood.
Mr Li is expected to end the NPC with a press conference on Sunday, given by Wen Jiabao for the past decade.
On Thursday, Xi Jinping's move was approved by 2,952 votes to one, with three abstentions.
Hours later, US President Barack Obama called both to congratulate him and raise concerns over ongoing issues, including cyber hacking and North Korea.
"Both leaders agreed on the value of regular high-level engagement to expand co-operation and co-ordination," a White House statement said.
Mr Obama is sending both Treasury Secretary Jacob Lew and Secretary of State John Kerry to Beijing in coming days, in an apparent bid to reach out to the new administration.
In an editorial, state-run Global Times said Mr Xi and his colleagues needed to show powerful leadership to unite society.
"China cannot stop developing or fighting corruption. Social unity is the key to how China can stand against complex international affairs," it said.