Current head of state Idriss Deby Itno — in power since 1990 after overthrowing former president Hissein Habre — is expected to be designated as candidate by his party, the Patriotic Salvation Movement, on February 6.
Deby, born in 1952, modified the constitution in 2004, scrapping its two-term limit on presidential tenure, and won the following elections by a huge majority.
Two opposition figures, Kassire Coumakoye and Malloum Yobode, have already declared they will run.
Candidates have from February 10 to 29 to file their bid. A runoff vote will be held on May 9 if no outright winner emerges from the first round in April.
Oil-rich Chad is playing a pivotal role in the military campaign against the Nigerian Islamist group Boko Haram.
On November 9, the government declared a state of emergency in the flashpoint Lake Chad region, which straddles Nigeria, Cameroon and Niger.