57-year-old Xi's promotion was announced at the close of the crucial Communist Party of China (CPC) plenum which also pledged to make "steady and vigorous" efforts to promote political restructuring, official Xinhua news agency reported.
Xi is expected to become the party chief in 2012 and later may take over from Hu as President in 2013.
His appointment could be a signal of a major reshuffle in China as along with President Hu, Premier Wen Jiabao and as many as seven of the nine current members of the key Politburo Standing Committee are expected to stand down in 2012 having completed two consecutive terms.
This will pave the way for a takeover by a new generation of leaders in a country that tends to work out succession in advance to prevent power struggles among senior officials.
The Chinese Vice-President is following Communist party tradition in the footsteps of Hu Jintao, who also became President and party chief after heading the Central Military Commission (CMC). The body oversees 2.3 million soldiers of the People's Liberation Army.
Though Xi was regarded as natural successor to Hu, doubts arose last year when he was not appointed to this post, setting off speculation that the all powerful President may have been backing someone else.
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