After graduating from West Point and being commissioned as an active duty Second Lieutenant, Tien was a Rhodes Scholar and earned a Bachelor of Arts degree from Queen's College, Oxford.

[4][13] Tien graduated from West Point on May 27, 1987, and was commissioned as a second lieutenant in the United States Army,[14] where he served for 24 years as an armor officer, retiring with the rank of colonel.

[17] Tien's other U.S. Army assignments included a two-year tour at the United States Military Academy as an assistant professor in the Department of Social Sciences where he taught American Politics from 1996 to 1998.

[18][19] From 2011 to 2021, Tien served in various roles at Citigroup to include being the chief operating officer for Citi Retail Services largest Mastercard and American Express co-branded card portfolios.

[22] On April 12, 2021, President Joe Biden announced his intent to nominate Tien to be the United States deputy secretary of homeland security under Alejandro Mayorkas.

[13][25] In September 2021, Tien represented the United States of America at the Group of Seven (G7) Interior and Security Minister's meeting where he was quoted as saying, "The United States is proud to stand with our G7 allies in our counterterrorism efforts and we look forward to continued cooperation to protect our nations from shared threats to our national security, as well as continued partnership to protect and support vulnerable Afghans.