In addition to working with small and mid-sized business clients since 1993, McCarthy was a consultant to NEC's Biglobe, the largest online service in Japan, from 1996 to 2001. His book The Internet Business Manual was the first book on web entrepreneurship published in that country. He is also credited by Hotwired magazine with being one of the people responsible for the development and popularization of the banner ad, one of the key underpinnings of commercial Internet publishing.

A graduate of Princeton University, McCarthy came to the Internet industry with a varied background which included technical consulting for two of New York's top investment banks, lecturing on educational psychology at MIT, Columbia, and NYU, and founding and operating a number of small businesses, including one that helped produce an Academy Award winning documentary.