Mahajan's first novel, Family Planning, was described by the San Francisco Chronicle as "Brave, breakneck, and amusing"'; in the Seattle Times as "Pleasurably crazed"; and in the Washington Post as "Genuinely funny" and "Profound". Author Suketu Mehta described it as "The truest portrait of modern New Delhi I’ve read, and the funniest book of the year", and novelist Jay McInerney called it "one of the best and funniest first novels I’ve read in years".

Family Planning was published by the Harper Perennial imprint of HarperCollins, and released in the US in 2008 and the UK in 2009, with translations forthcoming in India, Germany, Italy, Spain, France, Brazil, and Korea.

In 2003, Stanford University forced Mahajan and several other students to move out of their university-owned cottages so that they could be reserved for use as quarantine facilities for students with symptoms of SARS.

In 2004, Mahajan and two roommates opened a museum dedicated to Matthias K. Rath in their dormitory room at Stanford University.

Novels

• Family Planning ISBN 978-0061537257

Stories

• "The Cremation Ground" in Stumbling and Raging: More Politically Inspired Fiction ISBN 978-1596921580