Jeffry was a longtime attorney with the U.S. Environmental Protection Agency in the Boston/Region I Office, before retiring in 2017 and starting a new career as an adjunct professor. Initially while at the EPA, he specialized in water pollution law and served as chief of the water section in the Region I legal/enforcement office from 1982 to 1995. As part of that job, he served as the chief EPA attorney on the Clean Water Act enforcement litigation which finally resulted in the cleanup of Boston Harbor. During the second half of his career, Jeffry moved on to specialize in hazardous waste law.  In that capacity, he worked with the six New England states to update their hazardous waste programs, as well as being the attorney on various matters directly implemented by the EPA, such as issuing federal permits to hazardous waste facilities and making regulatory interpretations.

Jeffry became an adjunct professor in order to pass on the diverse perspectives he has gained on matters of environmental law and policy at the EPA. He hopes that his teaching helps students specifically interested in environmental protection, while also helping those preparing for careers in the environmental area more generally.

He has taught courses at the Golden Gate University School of Law, Northeastern University, and in the Tufts University Civil and Environmental Engineering department. At BC, he has been teaching the Seminar in Environmental Law regularly for the past several years, as well as a course in toxics law every other year at the Boston College Law School. He has been invited to teach a course in London in June 2023, comparing U.S. and European approaches to environmental law and policy. While his focus is on regulatory matters, more recently he has developed an interest in sustainability initiatives which go beyond what the statutes require.