MacQuarrie was last seen in Sarasota County, Florida on July 12, 2010. He left a phone message for a friend at 2:15 p.m., stating he was going to take his 26-foot open console pleasure craft with the operating number FL3292GM out on deep water on the Gulf. He said he would go snorkeling and would return by 8:00 or 8:30 p.m., but he never did and has never been heard from again. Two days later, the Coast Guard found his boat adrift and empty thirty miles offshore from Sanibel Island, south of Fort Myers, Florida. There was no sign of MacQuarrie at the scene. He left his home unlocked and left a float plan on the patio table.

MacQuarrie graduated from the University of Florida Law School in 1982 and was admitted to the Florida bar two years later, and practiced at a prestigious civil law firm. He got a divorce in the 1990s and following that ran into legal troubles, including three alcohol-related arrests between 1994 and 2004. In a bizarre incident in 2005, he was charged with holding three people, including his son and his legal secretary, at gunpoint at a rural farm in Reddick, Florida. MacQuarrie claimed he thought another lawyer with whom he shared office space was plotting to kill him, his family and the secretary. His defense stated he was delusional at the time and truly believe he was protecting himself and his loved ones. He was acquitted of all charges related to the incident, got his law license back, and resumed his practice. Most recently he lived in Siesta Key, Florida.

Authorities believe MacQuarrie was lost at sea. His body has never been recovered.