Lazar was born in in Montreal, Quebec. After graduating from St. George's High School she went on to study at Dawson College where she worked on the Daily Planet newspaper. After finishing college she moved to Boston, Massachusetts to attend Emerson College and obtained a BA in TV/Video production. Shira was the voice of the Peach in "Annoying Orange: Jalapeno ". She is the stepsister of American Apparel founder Dov Charney.
Lazar began her media career in 2004 as host of the College Sports Television program "1st Person". In 2005 she went on to become a host and producer for Music Plus TV and hosted celebrity Q&A video's on Yahoo. In 2006 she contributed feature pieces to Hollywood.com, and wrote that years Oscar's awards night preview feature for Los Angeles Confidential.
Lazar developed and hosted an online reality competition for MSN.com at TasteMaker. In 2009 she became the host of the Mahalo.com online weekly video program This Week in YouTube. In April 2008 Lazar began hosting "LX TV", a lifestyle entertainment show for NBC4 in Los Angeles.
Lazar currently covers the latest technology and media trends in a blog for CBSNews.com called OnTheScene. Lazar is a co-founder of the digital production company DISRUPT/GROUP, which produces online content such as The Partners Project, and interview show that profiles and features viral video stars. Lazar is also a regular contributor to The Huffington Post on issues of new technology, digital life and viral web trends. In 2009 Lazar was a featured writer and blogger on Travel Channel's "Confessions of a Travel Writer".
On May 17, 2011, Shira Lazar began hosting a weekly, live, interactive television show for the internet generation called "What's Trending" for CBS News. The show consists of two celebrity panelist discussing news that's currently trending or has been during the week. The show also showcases an interview with a top celebrity, one who has become influential through social media. Guests have included, Kevin Smith, Drew Carey, iJustine, Greg Grunberg, Talib Kweli, Alex Albrecht, Alison Haislip, Chris Sacca, Lisa Bettany, Weird Al Yankovic, Paul Feig, and Tony Hsieh, Chris Hardwick, and George Takei. Also during the program, Column Five Media creates info-graphics illustrating various topics such as, "How Something Goes Viral," and "The History of Video Games." The program showcases rising startups such as Games for Change, Pencils of Promise, Syyn Labs, and Getaround.
On June 7, rapper, producer Lupe Fiasco was interviewed during the program and said, "My fight against terrorism, to me, the biggest terrorist is Obama in the United States of America."  On June 20, Lupe Fiasco appeared on the Fox News show "The O'Reilly Factor" defending the controversial comments he made on the show.
Steve Rosenbaum of Huffington Post wrote an article that said, "It's clear that CBS is committed to this story -- jumping past the cheesy bluescreen or robo-set and building Lazar and her team a truly 'webified' set that is both high tech and modern. When the network springs for a set, you know they're in it for the long run." Mike Hale from The New York Times wrote on May 24, "What's really new about "What's Trending," and most of interest to Watchlist, is simply the fact that it's a live, scheduled half-hour Web show being done on the site of a major broadcast television network (and with a major corporate sponsor AT&T). That's revolutionary, whether the subject is social networking or retirement planning."