He was responsible for Immigration Policy and Programs that includes all immigration issues related to the admission and exclusion of aliens as well as the Agricultural Inspection at all Ports of Entry to protect the health of U.S. plant and animal resources and the facilitation of their movement in the global market place.

Additionally, he was responsible for Border Security and Facilitation, including Interdiction and Security, Passenger Operations, Targeting and Analysis and Canine Enforcement and for Trade Compliance and Facilitation which includes Cargo Entry and Release, Summary Operations, Trade Risk Management and Enforcement, and Seizures and Penalties as well as expanding Trade operations to focus on Anti-Terrorism.

Before the launch of the Department of Homeland Security on March 1, 2003, Ahern served in his current position with the legacy U.S. Customs Service since June 30, 2002.

Prior to that, he was the principal field manager of Customs port operations in Los Angeles, California, and Miami, Florida.

He has also completed intensive programs at Harvard University's John F. Kennedy School of Government and the Federal Executive Institute in Charlottesville, Virginia.