Additional District and Sessions Judge, K T Nisar Ahammed, also awarded double life imprisonment to another man in the case.
The Court had last week found Rani, a divorcee, and her two paramours, Ranjith and Basil, guilty in the killing of the woman's four-year-old daughter.
According to the prosecution, first accused Ranjith murdered the child in October 2013 as she became a burden on their relationship.
The Court found the first accused guilty under various sections of the Indian Penal Code and various sections of Protection of Children from Sexual Offences Act (POCSO Act) and awarded him death sentence.
Ranjith had allegedly consumed "othalanga," a poisonous fruit, on Wednesday after the Special Court found him guilty in the case.
The Court, which had posted the matter Friday to pronounce the quantum of verdict, had deferred the matter for today.