She quit the Congress earlier this month.
"I joined the BJP as I was influenced by Prime Minister Narendra Modi's ideals," Mohanty said.
The veteran actor left for bypoll-bound Bijepur assembly constituency later in the day.
Mohanty had unsuccessfully contested from Cuttack Lok Sabha seat as a Congress candidate in the 2014 general elections.
Her entry into the BJP comes a week after another popular Odia actor, Mahasweta Ray, joined the saffron party.
Two other eminent film actors, Anu Choudhury and Mihir Das, had joined the saffron brigade in January.