Garrels graduated from Harvard University's Radcliffe College in 1972. She subsequently worked at ABC in several positions for about ten years, including serving as Moscow bureau chief and correspondent until she was expelled in 1982, and as Central American bureau chief from 1984 to 1985. Garrels was the NBC News correspondent at the U.S. State Department. She joined NPR in 1988 and reported on conflicts in Chechnya, Bosnia, Kosovo, Afghanistan, Pakistan, Israel and the West Bank.Garrels was the Edward R. Murrow Fellow at the Council on Foreign Relations at the Council on Foreign Relations in 1996, and is a member of the board of the Committee to Protect Journalists.

Garrels was one of the 16 Western journalists who remained in Baghdad and reported live during the 2003 Iraq War. Shortly after her return from Iraq, she published Naked in Baghdad, a memoir of her time covering the events surrounding the invasion. She subsequently returned to Iraq several times for NPR. She was an embedded reporter with the U.S. Marines during the November 2004 attack on Fallujah. Garrels also covered the January 2005 Iraqi national elections for an interim government, as well as constitutional referendum and the December 2005 elections for the first full term Iraqi government. As sectarian violence swept much of central Iraq Garrels continued to report from Baghdad, Najaf and Basra.

In 2007 Garrels was criticised by FAIR for using confessions by prisoners who had been tortured during a story about an Iraqi Shiite militia (broadcast on NPR's Morning Edition). Garrels later defended her story on NPR's "Letters" program, saying: "Of course, I had doubts. But the details that were given seemed to me to gel with other things that I had heard from people who had not been tortured. But I was as uncomfortable as the listeners were with the conditions."

Garrels won a Courage in Journalism Award from the International Women's Media Foundation (IWMF) in 2003. In 2004 she was awarded the George Polk Award for Radio Reporting for her coverage of the war in Iraq.

Garrels is married to J. Vinton Lawrence, one of two CIA paramilitary officers from the Special Activities Division stationed in Laos in the early 1960s, who worked with the Hmong tribesman and the CIA-owned airline Air America. Garrels and Lawrence live in Connecticut.