Babis, who was previously prime minister from 2017 to 2021, promised Czechs that he "will fight for their interests at home and anywhere in the world" and will do his utmost for the Czech Republic to become "the best place for life on earth".
President Petr Pavel swore in Babis as prime minister on Tuesday.
Pavel had asked him to form a new government after his ANO, or YES, movement won big in the October 3-4 ballot and agreed to form a majority coalition government with two other small political groups, the Freedom and Direct Democracy anti-migrant party and the right-wing Motorists for Themselves.
The new partnership makes up 108 seats in the 200-seat lower house of parliament, relegating the four centre-right parties of the pro-Western government led by Prime Minister Petr Fiala to the opposition.
It was not immediately clear when Pavel might appoint the entire cabinet.
Its appointment is expected to change the government's policies.
The new coalition is set to follow Hungary and Slovakia, and steer the country away from supporting Ukraine in Russia's nearly four-year war.
The coalition members are critical of the European Union, rejecting its policies, particularly on environment and migration.
Babis, 71, still faces fraud charges in a case involving EU subsidies, and the new parliament will have to lift his official immunity for a court to issue a verdict.
After he lost the 2021 parliamentary election, he was beaten by Pavel, a retired army general, in a vote for the largely ceremonial post of president.
Babis was appointed after he met a condition set by Pavel and publicly announced that he would get rid of his major businesses to avoid a conflict of interest that could arise from his private dealings and his political status.
Babis owns about 200 companies under the Agrofert conglomerate.
He said an independent trustee will be in charge of Agrofert in a trust fund, while it will be under control of an independent protector until he dies, and then his descendants will inherit it.
Babis also owns a network of clinics and labs, while his close ally from ANO is a candidate for the hew health minister.
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