The daughter of Ranjit Mallick, Koel made her acting debut with Nater Guru (2003), which was a box office-success.

She rose to fame starring in commercially successful films Shubhodrishti (2005), Mon Mane Na (2008), Premer Kahini (2008), Rangbaaz (2013), Arundhati (2014) and.

Her performances in the family drama Bandhan (2004), the political thriller MLA Fatakeshto (2006), the drama Dui Prithibi (2010), the black comedy Hemlock Society (2012), the thriller Mitin Mashi (2019) received critical acclaim.

In addition to acting in films, Koel is a social activist and noted for her work with widows and children.

In the film, Mallick plays the role of a 23-year-old girl named Monica opposite Jeet.

[11] Mallick made her television debut with Zee Bangla's first Mahalaya in the year 2007 as Devi Mahisasuramardini and her various avatars.

[12] In 2013 Mallick appeared as a celebrity judge in the Bengali version of Jhalak Dikhhla Jaa along with Bollywood choreographer Remo D'Souza.

Mallick and Jeet were also seen as a guests in the Star Jalsha serial Sansar Sukher Hoy Romonir Gune for the promotion of the movie 100% Love.

Mallick has endorsed a variety of multi-national brands and has done television commercials for TVS Motor Company, glow & Lovely, Panasonic, and Vaseline.