Breen is a graduate of the University of Edinburgh and first began living in South Korea in 1982. He has covered North and South Korea for several newspapers including The Guardian and the Washington Times. In 1994, he became a management consultant specializing in North Korea, with clients such as Coca-Cola. He entered the public relations field in 1999 as the managing director of Merit/Burson-Marsteller. where he remained until 2004. He is now president of Insight Communications Consultants, a public relations firm. Breen was made an honorary citizen of Seoul in 2001.

As of May 2008, Breen has a featured column for The Korea Times, an English-language daily in South Korea, where he comments on Korean society, culture, and political issues. In December 2009, Breen wrote a satirical column in the paper which lampooned various South Korean public figures, including president Lee Myung-bak, entertainer Rain, and Samsung. Displeased with Breen's allusions to their corruption and arrogance, Samsung sued him and the paper for libel; the paper was later dropped as a respondent, but the suit against Breen himself remained.