He is a former consultant with The Boston Consulting Group. He was formerly an Outward Bound instructor. In 1984, Koch co-founded the Boston Beer Company, the producers of Samuel Adams beer.

Koch was married to Susan but had split up around the time that he launched the company. He remarried to entrepreneur Cynthia Fisher in 1994. He has two children from his first marriage and two from his second. They live in Newton, Massachusetts.

In 2016, Koch published Quench Your Own Thirst: Business Lessons Learned Over a Beer or Two, in which he discussed how he left his career as a management consultant to start his own brewery using his great-great-grandfather’s recipe.

In August 2018, Koch said the corporate tax cut of 2017 helped to play a major role in making Boston Beer Company more competitive in regard to foreign competitors. Koch stated that “When I started Sam Adams, American beer was a joke, and it pissed me off. And now, American brewers make the best beer in the world. And the tax reform was a very big deal for all of us, because 85 percent of the beer made in the United States is owned by foreign companies.”