Following law school, where Professor Johnson was Order of the Coif and the articles editor of the Texas Law Review, he clerked for both Judge John R. Brown, U.S. Court of Appeals, and Justice Hugo L. Black, United States Supreme Court. After the clerkships, his first teaching appointment was at the University of California Law School (Boalt Hall), Berkeley. He subsequently was an associate at the Washington, DC law firm of Covington & Burling, from which he was appointed by President Lyndon B. Johnson (no relation) to be the U.S. Maritime Administrator. He is perhaps best known for his tumultuous seven-year term as a Commissioner of the Federal Communications Commission (1966-1973), during which, among other things, he was featured on the cover of Rolling Stone magazine and published How to Talk Back to Your Television Set. He later served President Jimmy Carter as a presidential advisor for the White House Conference on Libraries and Information Services.
Professor Johnson has taught at a number of law schools (and communications studies departments), published widely in law reviews and general publications, and has taught law school courses ranging from administrative law, agency and partnership, constitutional law, and corporations to mass communications law and oil and gas law. His present teaching emphasis is on communications law in his courses Law of Electronic Media and Cyberspace Law Seminar.
Since his F.C.C. term, Professor Johnson ran for Congress, headed a Washington-based media reform group, hosted a PBS TV program, wrote a nationally syndicated column, consulted with numerous countries on media matters, and appeared at hundreds of colleges as a public lecturer. He is a Fellow of the World Academy of Arts and Sciences and a member of a number of non-profits' boards. He was co-director of the UI's Institute for Health, Behavior and Environmental Policy, and a member of the school board of the Iowa City Community School District. During 2008-09 he published four books: Your Second Priority, Are We There Yet?, Virtualosity, and What Do You Mean and How Do You Know?
Professor Johnson is a member of the law school's Intellectual Property Law faculty and of the supplemental faculty of the International and Comparative Law Program.
In 2009, Nicholas Johnson was selected as one of roughly 700 individuals described by Yale University Press as "leading figures in the history of American law, from the colonial era to the present day" included in The Yale Biographical Dictionary of American Law.