Xi, 64, was nominated by the Central Committee of the ruling Communist Party of China as a candidate for deputy to the 13th NPC, which was put to a vote at the regional congress, state-run Xinhua news agency reported.
The announcement of Xi's unanimous election at the first session of the 13th regional people's congress was welcomed with a thunderous applause, it said.
Xi was among 58 deputies elected to the new NPC at northern Inner Mongolia Autonomous Region's NPC session.
It is also a vivid demonstration of the loyalty to the core of the CPC and support of the people's leader by more than 1.3 billion Chinese from various ethnic groups, according to the deputies.
Xi also heads the party as general-secretary of the CPC, and the military besides the presidency.
The 13th NPC will open its first annual session in Beijing on March 5.