Mahathi began her playback singing career with Maestro Illayaraja. She recorded a solo Enna Maranthalum in his music direction in the movie Kaadhal Jaathi. Unfortunately, this movie did not see the light of day.
In 2003 Mahathi sang a duet, Aiyyaiyyo Pudichirukku, with Hariharan, under the music direction of Harris Jayaraj in Vikram superhit movie, Saamy.
Apart from film songs, Mahathi has sung many advertisement jingles, most popular being Pothys, Aachi Masala. She has also sung title songs for various serials in Vijay TV and Jaya TV.
In 2008, Mahathi won the Tamil Nadu State Film Award for Best Female Playback Singer for the song Naeraa Varattuma from the movie Nenjathai Killadhe
Mahathi has sung more than 700 songs in all various languages like Tamil, Kannada, Telugu, Malayalam and also Punjabi.