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Born and raised in Toronto, Rosen lived for a short time in Callander, Ontario. As a teenager he found a job at a men's haberdashery shop. There he learned about the composition of clothing and, more importantly, about men's shopping habits.
After dropping out of high school he borrowed $500 and opened a men's clothing store.
In 1961, the store moved to Toronto's downtown core on Richmond Street. That year Rosen met Stann Burkhoff, an advertising executive, and Burkhoff agreed to do some ads for the store in exchange for two suits — one for him and one for his art director. Together, they developed the 'Ask Harry' campaign. These ads ran in Canada's national newspaper, The Globe and Mail. It was so successful that people from across the country began coming to Harry Rosen.
Rosen frequently appeared in store advertisements in partnership with The Globe and Mail. One ad features Rosen having just locked up his store for the evening, when he notices one of his window mannequins reading the Globe and Mail; Rosen is also carrying a copy in his arm while there is also one of the newspaper's vending boxes in the background of the street.
When the original main store was burned down, Rosen took out an ad which was almost mistaken for an Obituary.
Rosen's ads based on political figures have sometimes been controversial.
Rosen has been active in the Canadian Paraplegic Association, Corporate Fund for Breast Cancer, Cancer Care Fund, Mount Sinai Friends for Life Campaign, Ryerson University Board of Governors, George Brown Board of Governors, University of Western Ontario Board of Governors, oDesign Exchange. He served a three-year term as Campaign Chairman for the Canadian Cancer Society, Metropolitan Toronto.
In 2004, he served on the Mt. Sinai Board of Governors, Ryerson B.Com program in retailing advisory board and on the Cabinet of Major Individual Gifts for the United Way of Canada.
He appeared in a promotional campaign for the Centre for Addiction and Mental Health to promote services for those affected by addiction and mental health issues in the Toronto area.
In April 2010 he was honoured at a fundraising event for The University Health Network called "Hats Off To Harry" 
- 1987 — Retail Marketer of the Year by the Retail Council of Canada
- 2001 — Retail Council of Canada's Lifetime Achievement Award
- 2003 — Honorary Doctorate in Commerce, Ryerson University
- 2004 — Order of Canada.
- 2005 — the Pitti Immagine Uomo Award from the Italian fashion community
- "Harry Rosen talks clothing in Ajax". Durham Region, Metroland Media. Keith Gilligan. Nov 08, 2015
- "Everything’s coming up Rosen: a Q&A with Toronto ‘fashion visionary’ Harry Rosen". Toronto Star, October 21, 2016. Jonathan Forani.
- "Harry Rosen on his keys to retail success". Orangeville Banner, Cassandra Szklarski. October 20, 2016.
- "Harry Rosen apologizes for ad featuring Donald Trump ". CTV News, November 25, 2015
- "Canadian Style Icons: Larry Rosen Has Fashion in His Blood". Huffington Post, 09/17/2013. Daniel Eckler
- "Hats off to Harry | Harry Rosen Tribute Dinner in support of a Regenerative Medicine Diabetes Chair at McEwen Centre for Regenerative Medicine, University Health Network | www.hatsofftoharry.ca". Tgwhf.ca. 2010-04-28. Archived from the original on 2012-03-01. Retrieved 2011-12-28.