Rebecca was born in Toronto to a family of Italian descent (her paternal grandparents were born in Caltanissetta) but she moved to Vancouver at age 2 and grew up there. She started playing tennis at age 10. In 2009, she moved to Montreal to train at the National Training Centre.
Marino played the first event of her career in Vancouver in 2005. In 2006, she played first round qualifying at the Rogers Cup in Montreal as a wildcard. Marino won in 2008 her first singles title in Trecastagni on the ITF Circuit and two doubles titles on the same circuit. She reached the second round for the second straight year at the 2009 Challenge Bell after a win in the first round over Lauren Albanese. Marino lost in the next round against Julia Görges.
Marino played the first Grand Slam of her career at the US Open. After winning three qualifying matches to enter the main draw, she beat Ksenia Pervak to set up a second round clash with world No. 4 Venus Williams. She lost after a thrilling and close first set which ended in a tiebreak. After the match, Venus said that now she knows what it is like playing herself. Her next tournament was in Quebec City at the Challenge Bell where she beat fellow Canadian Heidi El Tabakh in the first round. Marino upset first seeded and world No. 14 Marion Bartoli in straight sets in the second round, which was her first career win against a Top 20 player. She lost her quarter-final match against Bethanie Mattek-Sands. She then stayed in the province of Quebec and played a 50K Challenger in Saguenay the following week. Marino didn't disappoint her Quebecer fans as she made it to the final and defeated American Alison Riske in three tough sets to win the tournament. She won her second straight 50K Challenger in Kansas City by defeating Edina Gallovits in the final. One week later, Marino won her third straight 50K Challenger in Troy where she defeated Ashley Weinhold. She lost in the semifinals of the 50K Challenger in Toronto against Alizé Lim of France, stopping her winning streak at 18.
At the Australian Open, Marino defeated Junri Namigata in the first round. She lost in the second round against 6th seed Francesca Schiavone with a score of 7–9 in the third set. In February, Marino reached her first WTA tour final at the event in Memphis, where she faced Magdaléna Rybáriková. She was forced to retire from the match after losing the first set because of an abdominal strain. Marino qualified for the BNP Paribas Open, but lost in the first round to Ekaterina Makarova. Following her first round exit, Marino took part in the inaugural Bahamas Women's Open a $100,000+H event part of the ITF Circuit. As the fourth seed, she defeated qualifier Sophie Ferguson in the first round, Pauline Parmentier, and another qualifier, Heather Watson to reach the semifinals, where she lost against fifth seeded Angelique Kerber. At the French Open, she won her first round match over Kateryna Bondarenko and her second round match against María José Martínez Sánchez. She lost against 13th seed Svetlana Kuznetsova in the third round, her best Grand Slam result so far. The next month, she reached the second round for her fourth straight Grand Slam at Wimbledon where she lost to Roberta Vinci. At the US Open, Marino lost for the first time of her career in the first round of a Grand Slam to Gisela Dulko. She reached the quarterfinals of the Challenge Bell for the second year in a row, after beating fellow Canadians Stéphanie Dubois and Aleksandra Wozniak in the first and second round respectively, but lost to Michaëlla Krajicek. At the last tournament of her season, the BGL Luxembourg Open, she surprised the second seed and No. 15 player in the world Anastasia Pavlyuchenkova in the first round. That was the second win of her career over a Top 20 player. She lost her second round match against qualifier Bibiane Schoofs.
Marino lost in the first round of the 2012 Australian Open to Gréta Arn. She took a break from tennis to deal with mental and physical fatigue from February to late August. Marino made a comeback the second week of September at the $25,000 ITF in Redding. In only her fifth tournament since coming back, she defeated fellow Canadian Sharon Fichman to win the $25,000 ITF in Rock Hill. She then lost a week later in the first round of the $50,000 ITF Challenger in Saguenay to Maria Sanchez, stopping her winning streak at 8 matches. At the $50,000 ITF in Toronto, Marino was forced to retire in her second round match after suffering an abdominal strain. She was supposed to end her season at the $75,000 ITF in Phoenix, but had to withdraw following her injury.
At the 2013 Australian Open, her first Grand Slam since coming back, Marino made it to the main draw with her protected ranking of 115, but lost to Peng Shuai in the opening round. After playing some ITF and WTA tournaments, she decided in late February to take a second break from tennis with no timetable for her return.
Marino's win-loss record (3–16, 16%) against players who were ranked world No. 50 or higher when played is as follows:2010 – Tennis Canada female player of the year
2011 – Tennis Canada female player of the year
Players who have been ranked world No. 1 are in boldface.