In the early 1980s, Timmerman became a Middle East correspondent for The Atlanta Journal-Constitution and developed an expertise in arms trade.
[5] From 1985 to 1987, Timmerman was a correspondent for Defense and Armament Newsweek and Military Technology, covering the Iran–Iraq War and the arms industry in the Middle East.
He also wrote monographs for the Simon Wiesenthal Center on efforts by Iraq, Syria and Libya to acquire weapons of mass destruction.
In 1998, he wrote a piece on Osama bin Laden and his training camps in Afghanistan just before Al-Qaeda attacked two US embassies in Africa.
Timmerman wrote Shakedown: Exposing the Real Jesse Jackson as a change of pace from his focus on international issues in 2002.
[7] On February 7, 2006, Sweden's former deputy prime minister and Liberal party leader Per Ahlmark said that he had nominated Timmerman for a Nobel Peace Prize along with UN Ambassador John Bolton for "their repeated warnings and documentation of Iran's secret nuclear buildup and revealing Iran's repeated lying and false reports to the International Atomic Energy Agency.
[9] Timmerman was the 2012 Republican nominee for U.S. Representative for the newly redrawn Maryland's 8th congressional district, facing the incumbent Chris Van Hollen, a Democrat.