Manjima was a leading child artist in Malayalam film industry in early 2000's later she also hosted a television call-in show for kids by the name ‘Hai Kids’ on Surya TV for three years which rose her fame among Malayali audience.
Despite having had acting experience, she said that she was "not at all confident" when she started shooting for the film and that the initial days were "terrifying". Oru Vadakkan Selfie, which was directed by G. Prajith and scripted by Vineeth Sreenivasan, featured Manjima Mohan as the female lead.
Upon the release of Oru Vadakkan Selfie, Manjima landed her first Tamil film, Achcham Enbadhu Madamaiyada. Its director Gautham Menon, who was impressed with her work in Oru Vadakkan Selfie, cast Manjima as the female lead, after she had gone through an audition.
In 2017 she had two Tamil Films opposite to Udhayanidhi Stalin and Sathriyan opposite to Vikram Prabhu. In 2019 , she made her come back to Malayalam with Mikhael opposite to Nivin Pauly for the second time. She has replaced Amala Paul in Zam Zam , official remake of Queen. She also has a few Tamil films in her kitty.