Governor D.Y. Patil administered the oath of office to Lessi Singh at the Raj Bhavan. Nitish Kumar, assembly Speaker Uday Narayan Chaudhary and others attended the function.
Lessi Singh's induction is the first expansion of the cabinet after the ruling Janata Dal-United (JD-U) ended its 17-year-old alliance with the Bharatiya Janata Party in 2013.
The JD-U legislator from the Damdaha assembly seat in Purnea district was inducted a day after industry and disaster minister Renu Kumari Kushwaha resigned from the cabinet citing personal reasons.
With the chief minister accepting Kushwaha's resignation on Tuesday, there is no woman left in the cabinet.
Nitish Kumar's statement that he would expand the cabinet after the polls has disappointed several legislators who were eyeing a berth in the council of ministers.