Jethmalani is a granddaughter of businessman Shyam Jethmalani. Her childhood pet name is "Dinky". Her mother Divya is a housewife and her father Nimesh Jethmalani is a businessman. She has two siblings- brother Kapil and sister Karishma. Kamna is granddaughter of Ram Jethmalani. She was the runner-up at the Miss Mumbai contest in 2004 and also appeared in the music video of the pop song 'Chhod do Aanchal Zamaana Kya Kahega' by Bombay Vikings. On 11 August 2014, Kamna married Suraj Nagpal, a Bangalore-based businessman.

She appeared in the video of "Chhod Do Aanchal Zamaana Kya Kahega" by Neeraj Shridhar – Bombay Vikings in 2004. The following year, she made her movie debut with the Telugu film Premikulu. Though that film flopped, her second film Ranam was a big hit. Her first Tamil film was Idhaya Thirudan with Jayam Ravi. She did an item number in the film Sainikudu. She has acted in Machakaaran opposite Jeevan. Since then, she has done several south Indian films, in which she performed the lead role.