Foster was one of broadcasting's great promoters and showmen and the founder of Foster Advertising Limited. He was also one of Canada's great humanitarians. He had a passion for sport and was involved in playing, coaching and managing. On the side, he started selling advertising on sports programs which he wrote and printed. Wrestling and radio were becoming popular and Foster brought the two together. On April 11, 1931, he made his first live broadcast from a wrestling match. That was the start of a new era in radio in which every sports event was soon tied to sponsorship. He sold the ads on his shows, wrote the copy, printed the programs, did the commentary and read the commercials, frequently from the rooftops or rafters. In 1931, he claimed the first coast-to-coast football broadcast. It originated at Molson Stadium in Montreal from where it travelled to CKGW Toronto and on by phone lines to Vancouver and to Sydney, N.S. Three years later he broadcast the Grey Cup final from Toronto to a full network. The same year, he incorporated as The Harry E. Foster Agencies Limited. He organized the first televising of a Grey Cup game for the CBC in 1952 and coverage for CBC-TV of the 1954 Commonwealth Games in Vancouver and the Grey Cup final that year. In 1955, the CBC outbid the private industry and started its own sports coverage. After that, Foster's agency concentrated on advertising and promotions rather than programming. His younger brother, Jackie, had Down's syndrome and was blind. It was Foster's idea to launch CFTO-TV Toronto in 1961 with an 18-hour telethon on behalf of the mentally handicapped. In retirement, he devoted his life to helping charities. The first Special Olympics in Chicago in 1968 were the result of the research into fitness among the mentally disadvantaged, and Foster took care of Canada's participation and supported the games until they became established in Canada. Among his many awards were the Medal of Service of the Order of Canada, an honorary doctorate, the Kennedy Family Award, an Ontario Special Achievement Award, the Queen's Jubilee Medal, a Broadcast Executives Society Achievement Award, and a B'nai Brith Humanitarian Award. He was inducted as a builder into Canada's Sports Hall of Fame in 1984. Paul E. Lewis wrote a 1994 biography "Ladies and Gentlemen, Mr. Harry 'Red' Foster".
In 1998, Foster was remembered by Canada Post with a special stamp. He died in 1985.