On the football field, Jim Marcellino was one of Greater Boston’s legendary running backs, running for four touchdowns on Thanksgiving Day in 1961 during his final game at Archbishop Williams High School and scoring the game’s only touchdown two years later as he led the College of the Holy Cross to an upset win over Boston College.

When Mr. Marcellino was presented with the O’Melia Award as the game’s outstanding player, Holy Cross football coach Eddie Anderson said he was “one of the truly great backs of the country. He plays defense and offense. He blocks and tackles. He carries the ball. And he does them all outstandingly.’’

Just as quick in the courtroom, though with his mind rather than his feet, Mr. Marcellino became president of the Boston Bar Association in 1993 and was known for his prowess as an attorney specializing in intellectual property litigation.

“When you stand up to open to a jury, you’re the first witness for your side,’’ he told Boston Business Journal for an interview published in 2008. “The secret of being a good trial lawyer is understanding that demeanor is testimony. When you go to the courthouse, you have to assume that everyone’s eyes are on you. What you do and how you do it becomes very important.’’

Mr. Marcellino, who was a fellow of the American College of Trial Lawyers, died of renal failure June 30 while in hospice care. He was 73 and had lived in Milton.

“He was a giant in the profession in every way you think of,’’ said Melissa Nott Davis, a partner at McDermott Will & Emery, where Mr. Marcellino worked for many years. “You couldn’t walk down the street with him without running into people who knew him. Juries loved him and judges loved him. He just lit up the room.’’

She added that Mr. Marcellino “was incredibly smart and had a great legal mind. You wanted to learn from Jim. He gave you a lot of guidance as a mentor, but he gave you some room because he wanted you to figure it out.’’

As part of a tribute sent to Boston Bar Association members, former executive director Frank Moran wrote that Mr. Marcellino’s term as president “was a reflection of his philosophy that the practice of law should be civil and fun. His effusive and engaging personality and sense of humor transcended all his activities, professional and personal.’’

Indeed, in an association publication from fall 1993, Mr. Marcellino encouraged colleagues to “ ‘chill out’ a bit’’ and added: “Plain old fun can be a leavening ingredient in all of our activities. Let’s make it a requirement.’’

Born in Brighton, James J. Marcellino was the second of six children. His father, William, worked in the insurance business and was involved with politics. His mother, the former Mary Long, was a homemaker.

Growing up in Quincy and Milton, Mr. Marcellino was “a super student,’’ said his sister Mary Marcellino Zouberis of Methuen. “He studied, but it came pretty easy.’’

At Archbishop Williams High School in Braintree, he was all but untouchable as a running back. When he chose to attend Holy Cross in 1961, the Globe reported that he was the state’s most sought-after schoolboy football player. Touchdown runs of more than 50 yards were almost commonplace for Mr. Marcellino.

Yet he also “loved poetry and could quote Whitman, Coleridge, Robert Frost,’’ said Damian Pettinelli of Randolph, a friend since childhood. “He was more than what he seemed.’’

Though Mr. Marcellino continued to be a football standout at Holy Cross, “he always went out of his way to help somebody he perceived was in trouble,’’ said David Drohan, who was his college roommate for three years and is a founding partner of Drohan Tocchio & Morgan.

“When he became a star, he was the one down talking to the freshmen and sophomores to make sure they felt comfortable,’’ Drohan said. “He was a very decent human being.’’

After graduating from Holy Cross, Mr. Marcellino tried out for what was then the Boston Patriots and recalled playing in an exhibition game against Joe Namath and the New York Jets before his football career ended. “I jokingly say I was cut with plenty of time to spare to make my first class in law school,’’ he told the Boston Business Journal.

He graduated from Boston College Law School and provided legal services to a Detroit neighborhood through the Volunteers in Service to America program before launching his career. He also received a master’s in business administration from Boston University.

Along with practicing at McDermott Will & Emery, he formerly was counsel to the firm that was then Hanify & King, and he was a partner at the firm that was known as Gaston & Snow when it dissolved in the early 1990s. Mr. Marcellino formerly was a project director and attorney for the Boston Redevelopment Authority and a deputy and special assistant attorney general. He had taught at Boston College Law School and was an aide for political campaigns in the 1970s and ’80s.

In 1982, Mr. Marcellino married Stacey Baker.

His rise to a partnership at Gaston & Snow came “at a time when people with vowels at the end of their names didn’t become partners in major Boston firms,’’ Drohan said.

“He had a terrific reputation as a trial lawyer,’’ said Donald R. Frederico, a partner at Pierce Atwood who had worked with Mr. Marcellino at McDermott Will & Emery. “He had a great instinct for how to address a group of people. He was very good at taking complex issues and making them easy to understand.’’

A service has been held for Mr. Marcellino, who in addition to his wife and sister leaves his son, James of New York City; his daughter, Marianna of South Boston; three brothers, William of Brick, N.J., Richard of North Quincy, and Jocko of La Jolla, Calif.; and another sister, Sister Noella of Bethlehem, Conn.

“He had that ability to capture people emotionally and you wanted to be his friend,’’ Davis said. “He absolutely had that.’’

Mr. Marcellino also could reduce the complexity of a law career to some simple advice. “Do some good, learn some things and have some fun. That’s a good day,’’ he told the journal.

He was even able to shrug off the ribbing of those who poke fun at attorneys, but he generally drew the line at joining in. “The problem is if lawyers go around telling lawyer jokes, it’s a tacit approval of them. There are lawyers who are really combative about this,’’ he told the Globe in 1993, adding with a laugh: “I have trouble delivering them, and my delivery otherwise is impeccable.’’

Marquard can be reached at bryan.marquard@globe.com.