Sethi began her media career in 1993 as a documentary producer for MTV News. In 1994, she became a reporter/producer for MTV Networks Asia News, eventually taking the anchor chair in 1995. She co-created and ran the news department for MTV India in 1996. Sethi anchored and produced their news broadcast until 1997, after which she developed her own production company, SHE TV.

Sethi returned to the United States in 1999 and hosted Daily Remix for Oxygen Media. After working as a consultant for business and activist groups, she became the anchor/writer for the public television series Ethical Markets. Sethi is the contributing author (with Hazel Henderson) to the companion book for that series, Ethical Markets: Growing the Green Economy which was awarded a 2007 Nautilus Silver Book Award for Business/Conscious Leadership and a 2008 Axiom Bronze Business Book Award for Business Ethics.y

Sethi co-created, hosted, and oversaw all video and audio content as executive producer for TreeHugger.com, the largest environmental website on the Internet. Under her management, TreeHugger won the 2006 Vloggie for Best Green Vlog.

Lauded in Vanity Fair: The Green Issue as "The Green Messenger", Sethi hosted a forum on global warming with Nobel Laureate Al Gore for Al Gore on Live Earth and created an audio podcast series called Tune In: Podcasts About How You Can Make a Difference for Gore's non-profit The Alliance for Climate Protection. She has been identified in Vanity Fair's Women's Impact Report as an environmental woman of impact, alongside Laurie David, Julia Louis-Dreyfus, and Sheryl Crow. Sethi was also named one of the top Eco-Heroes of the Planet by the UK’s Independent in July 2007, made the 2008 Best Dressed Environmental List, and was featured on Earth First's 2008 Who's Who in Green List.

Sethi has appeared as an environmental expert on various TV programs including The Oprah Winfrey Show, The Ellen DeGeneres Show, and Martha. She has contributed to NBC Nightly News, MSNBC, CNBC and The Today Show, and wrote/hosted the Powering the Planet series for CNBC. She is the creator of The Sundance Channel web series The Good Fight, highlighting global environmental justice efforts, and, along with Majora Carter, was the founding host of The Sundance Channel's environmental block The Green. Sethi formerly served on the board of advisors for New York City-based NPR station WNYC, and on the board of directors for the National Radio Project. She is the 2009 recipient of the Smith College Medal, awarded to alumnae demonstrating extraordinary professional achievements and outstanding service to their communities. In 2010, Sethi was awarded the 2010 Champion of Sustainability Award from the American College

As an associate professor at the William Allen White School of Journalism & Mass Communications at the University of Kansas, Sethi teaches courses on sustainability and environmental communications. She currently serves on the Sustainability Advisory Board for the City of Lawrence, Kansas, and is the former chair of the City’s working group on climate change policy, education and outreach. Sethi is currently a contributing editor for Mother Earth News. She is also working on a book about the psychological barriers to environmental engagement to be published by Harper Collins. Sethi has created a series of blog posts on products' life cycles and the impacts of everyday consumption for The Huffington Post and wrote about her eco-friendly home renovations for Oprah.com. Her posts are also featured on The Healthy House Institute website, and she serves on HHI's advisory board. Sethi also serves on the advisory board for the Glynwood Institute for Sustainable Food and Farming.

Sethi graduated cum laude in 1992 from Smith College with a BA in sociology and gender studies. In 2005, she was awarded an MBA in sustainable business by the Presidio Graduate School San Francisco.