But to his family, friends and fellow workers, who filled St. Patrick's Cathedral in Manhattan Friday, McNamara was a good-natured prankster, devoted husband and father who always led by example.
"He was one of the best people I have had the pleasure of knowing," friend Christopher Mullin said. "He did what was right, not what was popular."
McNamara, 44, worked about 500 hours at Ground Zero. He was diagnosed with colon cancer in 2006 and believed his exposure to toxins on the pile caused the illness that ultimately killed him Sunday.
"John may not have died on 9/11, but it was the work there that killed him," said his wife, Jennifer, who is urging Congress to bring a 9/11 health bill to a vote.
McNamara's coffin arrived at the cathedral on a police-escorted fire engine in a procession typically given to firefighters killed in the line of duty. More than 200 firefighters and police officers stood at attention.
During the funeral Mass, FDNY chaplain the Rev. Christopher Keenan held the four-pronged tool McNamara used to rake 9/11 debris to illustrate his determination.
"He searched for each human person with dignity," Keenan said. "He lived life to the fullest in the face of death."
Mullin described a colleague who was always cracking jokes and would fondly "break your chops" at the Engine 234 station house in Crown Heights, Brooklyn where he worked.
McNamara's body will be cremated.
Jennifer McNamara said that for her husband, being a firefighter, not only with FDNY but also as a volunteer with the Blue Point Fire Department, was the "essence of who he was."
It was his son, Jack, 3, however, for whom he fought hardest, looking into every treatment possible so he could spend as much time as he could with him, she said.
He played house dad, changing diapers, feeding him, playing with him, watching baseball together and reading as she worked, McNamara said.
And while Jack is too young to comprehend his father's illness and death, it was not completely lost on him: He would pat him on the back and say, "Feel better, Daddy," she said.