Petrillo's grandparents emigrated to Canada from Italy. When she was 19, Petrillo began volunteering at her local television station, Rogers Cable York Region in Ontario Canada. She worked behind the scenes on various shows from sports, news, politics, to entertainment. Finally, Petrillo was given an on-air opportunity on the magazine show 'York Region Living,' where she hosted the restaurant segment. Petrillo has often joked about her first on-camera gig: "Figures, as someone of Italian heritage, my first opportunity would come as a restaurant reporter. I got paid in food!" Petrillo's role began to grow at the station and in 2004 the title of Sports Host and Producer became available. The station manager at the time, Lisa McClean Stellick, wanted Petrillo as her sports host, but was met with some push-back by some executives who were concerned about having two women at the desk for the nightly newscast, as the main news host was Jennifer Buchanan. McClean Stellick prevailed and in 2004 Petrillo became the sports host and producer for York Region. She covered various sports and found her niche in hockey where she hosted a weekly live Junior 'A' hockey broadcast.
In 2006, Petrillo joined Leafs TV (owned by Maple Leaf Sports and Entertainment (MLSE)) and served as a reporter for broadcasts of games featuring the National Hockey League's Toronto Maple Leafs and their American Hockey League affiliate, the Toronto Marlies, respectively. With ESPN, she had the opportunity to do some freelance work such as sideline reporting for the 2008 National Lacrosse League championship game. Petrillo's role expanded under MLSE, and she began working on their other television stations: NBA TV Canada and GOL TV Canada as host and reporter for the Toronto Raptors and Toronto FC games.
In 2010, Petrillo travelled to Haiti on behalf of MLSE to deliver supplies after the earthquake. She then went to Afghanistan, along with former NHL players and the Stanley Cup to help lift the morale of the soldiers.
Petrillo joined Hockey Night in Canada for the 2011-12 NHL season and hosted the iDesk portion of the broadcast, becoming the first female to serve on a full-time basis with the HNIC studio team. She anchored CBC's coverage of the 2014 Winter Olympics in Sochi Russia, and the 2014 FIFA World Cup. Petrillo then joined NHL Tonight, the flagship show on the NHL Network in Canada and the United States, for the 2014-15 NHL season.
On October 24, 2015, CBC Sports launched a new show 'Road to the Olympic Games,' which Petrillo co-hosts with veteran sportscaster Scott Russell. CBC owns the Olympic rights in Canada until the 2024 Games, and the show features elite high-performance athletes.
On February 18, 2016, it was announced that Petrillo joined TSN as the new radio voice for Leafs Lunch on TSN 1050, becoming the first-ever woman in Canada to have her own daily sports talk radio show.
Petrillo will remain with CBC as one of their Olympic hosts.
Petrillo was a pre-game host for MLS Cup 2016.2012 Woman of Influence Award (presented at the CIS Women's Basketball Final 8)
2015 Best Sports Host in a Sports Program or Series for her work during CBC Sports' coverage of the 2015 Pan American Games. Petrillo becomes the first woman honoured by the Academy of Canadian Cinema & Television with an award as a host in a sports program or series.