In April 2009, Muir teamed up with Sawyer for a primetime hour on guns in America. Muir and Sawyer revisited the issue in 2014 with their hour, "Young Guns." In March 2009, his reporting on "20/20" revealed the growing ranks of homeless children in America. During the 2008 presidential election, he was part of the network's "Vote 2008" coverage, reporting and anchoring from Iowa, New Hampshire and South Carolina, and reporting from Ohio on Election Night. Muir reported from Pennsylvania Avenue on Inauguration Day.
Overseas, in August 2008, Muir reported on the aftermath of the earthquake that devastated China's Sichuan Province. He reported from the Israeli-Lebanon border in August 2006, where he covered the Israeli war with Hezbollah. He was also in Gaza in June 2007 to cover the Hamas coup, reporting from inside the Gaza Strip. In August 2007, he was sent to Peru to cover the worst earthquake in that country in more than 35 years, and in March 2008, he reported from Ukraine more than two decades after the Chernobyl nuclear accident.
Muir anchored and reported from the 2010 Winter Games in Vancouver and the 2008 Summer Olympics in Beijing.
In August 2005, he was inside the New Orleans Superdome as Hurricane Katrina hit, and stayed in that battered city to cover the unfolding crisis. His reports for "World News" and "20/20" were the first to reveal the deteriorating conditions inside the Convention Center and Charity Hospital, as he waded through chest-deep waters to get to the patients still inside the hospital. In October 2006, he was on the scene of the Amish schoolhouse shootings in Lancaster County, Pennsylvania. He also reported from West Virginia on the letters left behind by the coal miners during the Sago Coal Mine tragedy for "20/20."
Muir has contributed to several in-depth series on "World News," including "Going Home," "The Fight to Save the Middle Class" and the broadcast's "Key to Success" series, reporting on efforts to revitalize Yosemite National Park.
Shortly after joining ABC, Muir anchored ABC News' coverage of the ceremonies marking the 60th anniversary of D-Day, and in his first week on the air anchored several hours of the network's coverage of the Blackout of 2003.
Prior to joining ABC News, Muir distinguished himself as an award-winning anchor and correspondent for WCVB-TV, the ABC affiliate in Boston. He spent a month in the Middle East reporting on the war in Iraq, helping to earn the station the prestigious National Headliner Award. He spent several weeks in Florida reporting on the 2000 Presidential election recount, and reported extensively on the sexual abuse scandal within the Boston Archdiocese.
While in Boston, Muir was part of the team that received the regional Edward R. Murrow Award for investigative reporting and Associated Press honors for his work tracing the path of the September 11th hijackers. His anchoring and reporting of breaking news in Boston earned top honors from the Associated Press.