Garrett has both a Bachelor of Journalism degree and Bachelor of Science degree in political science from the University of Missouri from 1984. He is a member of the Fraternity Phi Gamma Delta.

Garrett was a senior editor and congressional correspondent for U.S. News and World Report and a congressional reporter for The Washington Times in the 1990s before joining CNN's White House team in early 2000, and later moving to Fox in 2002 as a general assignment reporter. There, he covered the 2004 election, and served as the network's congressional correspondent. He has also been a White House correspondent for CNN, and an award-winning reporter across the country for Houston Post, Las Vegas Review Journal, and Amarillo Globe-News. His articles have appeared in such magazines as The Weekly Standard, Washington Monthly, and Mother Jones. He currently lives with his family in Washington D.C.

Garrett covered Barack Obama's presidential campaign. On January 13, 2009, Garrett became the senior White House correspondent for the Fox News Channel.

Garrett announced that he would be leaving Fox News on September 3 to join National Journal.. His final day on Fox News was on America Live Youtube