Ohman worked as a political aide for the Minnesota Democratic Farmer Labor Party (DFL) during his high school years in Minnesota. At age 17, Ohman worked at the Minnesota Daily, the student newspaper of the University of Minnesota. At age 19, Ohman was the youngest cartoonist ever to be nationally syndicated. Slate Magazine - Editorial and Political Cartoons, Comic Strips His first daily newspaper job was at The Columbus Dispatch, where he was hired in 1981. He then moved to the Detroit Free Press in 1982, and went to The Oregonian in 1983.

Ohman was a regular art contributor to ABC News Nightline in 1984.

In 1986, through the sales of copies of his cartoons on the space shuttle Challenger accident, Ohman raised over $30,000 for the families of the astronauts. It was the fifth largest private donation in the United States. In 2001, he raised over $30,000 for the United Way September 11 Fund.

Ohman has an honors degree in U.S. history from Portland State University. He is an adjunct associate professor of political science at the Mark O. Hatfield School of Government at Portland State University. He was a regular contributor to Foreign Policy and Money magazines. Ohman is also the creator of the syndicated comic strip Mixed Media, which appeared in over 170 newspapers.

In 2006, Ohman was voted one of the top five cartoonists in the United States by the readers of The Week magazine.

His work regularly appears in most major U.S. newspapers including The New York Times, Chicago Tribune, The Washington Post, The Philadelphia Inquirer, and The Seattle Times. He has also been featured in many magazines and high-profile websites. Ohman is also a noted fly fishing humorist, and has published four books on the subject, including the best-selling Fear of Fly Fishing, "Get The Net," "An Inconvenient Trout," and "Angler Management," a book of essays. He has published 10 books overall.

Ohman has won the 1980 Sigma Delta Chi Mark of Excellence Award, the 1995 Thomas Nast Award from the Overseas Press Club, the 2001 Harrison E. Salisbury Award from the University of Minnesota, the 2002 National Headliner Award, the 2009 Robert F. Kennedy Journalism Award, and the 2010 Society of Professional Journalists Award.