Pro-tem Speaker Niranjan Debbarma announced that the 60-year-old lawyer-turned politician was elected unanimously as there was no other candidate for the post. Debnath has held the post since 2003.
Debnath, also a former minister, was elected to the Tripura assembly uninterruptedly for the fifth time in the Feb 14 election from Yubarajnagar.
A week-long session of the newly assembly began on Friday with the customary speech of Governor D.Y. Patil.
Finance Minister Badal Chowdhury presented a vote-on-account for the first three months of the 2013-14 fiscal.
A full-fledged budget for 2013-14 would be presented within the next three months, Mr Chowdhury told IANS.
Scripting a record, this would be Mr Chowdhury's 16th budget.
The Left Front led by the CPI-M (49 seats) and including the Communist Party of India (one seat) won 50 of the 60 seats. The Congress won only 10 seats.