Mac is the leader of the CSI team in the New York area.
Mac's father died of small-cell lung cancer and spent the last eight months of his life in bed on a feeding tube. As a result, Mac has come to believe strongly in a person’s right to a dignified death. However, when his father begged him to pull the plug, Mac couldn’t do it.
Mac was married to Claire Conrad. They had no children together, though Claire had a child (Reed Garrett) from a previous relationship, who she had since put up for adoption. Mac once described Claire as athletic, with curly brown hair and big blue eyes. Claire was killed in the 9/11 attacks and her death troubles him to this day, causing chronic insomnia. After her death, Mac got rid of everything that reminded him of her, except pictures and a beach ball she had blown up, saying, "Her breath is still in there". Her remains were never recovered from the debris of the World Trade Center.
He served as a lieutenant in the U.S. Marine Corps, once saying that he had wanted to serve the country more than anything else in the world. He served in Beirut in 1983, from which he still bears a scar over his heart. Mac will protect three things at any cost: the honor of his country, the safety of his city, and the integrity of his lab.
Thanks to his Marine training, he is skilled in unarmed defense and seems to have an intimate knowledge of a wide range of weaponry, from bows to East Asian weaponry to the more everyday guns and knives. To Mac, the type of weapon used is as revealing as anything else at the scene of the crime.
Mac has a close friendship with Stella Bonasera and plays bass guitar at jazz clubs during his off-time. This talent was discovered by Lindsay Monroe when she observed, during an investigation, that he knew how to hold the instrument.
