Observers say the appointment is most likely a reward after Pahimi Padacke announced his support Friday for President Idriss Deby Itno, who is running for a fifth term in April elections.
Outgoing prime minister Kalezeube Pahimi Debeu, in power since 2013 and a member of the ruling Patriotic Salvation Movement (MPS), resigned from the post.
The radio broadcast Saturday did not give any further details, but the new prime minister is leader of the National Rally of Chadian Democrats (RNDT), a political party aligned with the MPS, and came second in presidential elections in 2011.
President Deby, who has been in power for 26 years, modified the constitution in 2004, scrapping its two-term limit on presidential tenure, and won the following elections by a huge majority.
Deby had seized power in 1990 after toppling Hissene Habre, who is on trial at a special court in Senegal for crimes against humanity. Habre, 73, was president of the oil rich but poverty-entrenched country from 1982-1990.
An investigating commission found that more than 40,000 people were killed during his rule, which was marked by fierce repression of his opponents and the targeting of rival ethnic groups.
A verdict is due in May and Habre could be sentenced to life imprisonment with forced labour.