Voss was a member of the New York City Joint Terrorism Task Force from 1986 to 2000 He was involved in monitoring the New York City landmark bomb plot after spending three years investigating the 1993 World Trade Center bombing. He was the "co-case agent" during the investigation of the 1996 TWA Flight 800 explosion.

In 1992, he received hostage negotiation training at the FBI Academy. He spent 24 years working in the FBI Crisis Negotiation Unit and was the FBI's chief international hostage and kidnapping negotiator from 2003 to 2007.‍

In 2006, he was the lead negotiator on the Jill Carroll case in Iraq as well as the Steve Centanni case in the Gaza Strip. Voss supervised additional hostage cases in the Philippines, Colombia and Haiti.

After working on more than 150 international hostage cases, he retired from the FBI in 2007 and founded The Black Swan Group. The Black Swan Group serves as a consultancy and trainer for both businesses and individuals on negotiation skills. He became an adjunct professor at Georgetown University's McDonough School of Business and a lecturer at the USC Marshall School of Business.

In 2016, Voss co-authored the book Never Split the Difference: Negotiating As If Your Life Depended On It, with journalist Tahl Raz.

Voss was given the Attorney General's Award for Excellence in Law Enforcement as well as the FBI Agents Association Award for Distinguished and Exemplary Service.

Voss is a regular commentator on CNBC, CNN, MSNBC, and Fox News, and NPR.He has also been featured in Forbes, The New York Times, Inc., Variety, and Time.‍

In 2019, he created and narrated a MasterClass, The Art of Negotiation.