Marshall last night told an audience of roughly 250 students about his battle with Borderline Personality Disorder (BPD). He described how pressure, the NFL, and fame changed him, how the intense emotion and ferocity that made him successful started to ruin him, how he gained the skills to cope with mental illness through intensive therapy. He traced his journey from what he called a “ticking time bomb’’ to a “tamed Beast.’’

“The Beast was out of control,’’ said Marshall, using his nickname. “The Beast was scary at times. The Beast was untamed. The monster can still think with that same emotion, that same passion, but he has a switch.

“When I touch the field, I turn on the switch. I play with a lot of passion, a lot of emotion, the way the game is supposed to be played. But now, I have the ability to turn that switch off when the clock hits zero. The monster is controlled.’’

Throughout the school year, Harvard hosts plenty of famous speakers, from politicians to entrepreneurs to artists who stand out in their fields. But an active NFL player speaking during the middle of the season is a rarity. The candid talk Marshall gave about mental illness made the event all the more unique.

Diagnosed with BPD at McLean Hospital this past spring, Marshall now commits himself to playing football, continuing therapy, and educating others about his illness. The Mayo Clinic defines BPD as “an emotional disorder that causes emotional instability, leading to stress and other problems.’’ BPD distorts a person’s self image, the Mayo Clinic description continues, and makes that person “feel worthless and fundamentally flawed.’’ Symptoms include “anger, impulsivity, and frequent mood swings.’’

At a time when mental illness still carries a stigma, Marshall is eager to speak up, raise awareness, and push for more research. He said he hoped to “break the stigmas associated with mental illness,’’ and told the students to “take the good out’’ of his story and to get help if they need it.

“Without the help of McLean Hospital, I wouldn’t have had the ability [to turn on and off the switch],’’ said Marshall. “Honestly, I probably would be out of the NFL and I probably would be divorced. I don’t want to even think where I would be after that.’’

Before Marshall understood what he faced in BPD, he earned a reputation as a volatile, unpredictable player with extreme emotional outbursts. He lost a good friend and former teammate, Denver Broncos cornerback Darrant Williams, in a New Year’s Day 2007 shooting that was, according to witnesses, preceded by arguments between Marshall and the convicted shooter. And he almost destroyed his marriage.

Last April, after an incident at the couple’s home in which authorities determined Marshall was stabbed, the police, as Marshall described it, “wrongfully arrested’’ his wife, Michi Nogami-Marshall. Brandon Marshall insisted he fell on some broken glass.

The bizarre, headline-making incident was the low point of Marshall’s battle with mental illness. But it brought him to McLean for the diagnosis and intensive treatment. “It was my ‘ah-ha’ moment,’’ said Marshall of learning why he struggled to control his emotions and why he felt unhappy despite signing a $50 million contract with the Dolphins last year. He felt a “tremendous weight lifted.’’

Since his diagnosis, Marshall has learned coping strategies and talks with doctors at McLean via Skype on a weekly basis. He does not take medication, but rather works on being mindful of his triggers, on keeping the criticisms of others in perspective, on staying positive, on expressing himself more fully. He also uses church as therapy and relies on the support of friends, family, and, especially, his wife.

With the Dolphins 0-6 this season and the locker room tension mounting, Marshall relies on all he has learned through therapy. Before the Dolphins played the New York Jets recently, Marshall was unhappy with the game plan. And he put his new coping skills to work. He took out his playbook and told his wife what was wrong with the planned strategy.

“We had 70 plays in our playbook and I went through every single one of them,’’ said Marshall. “Halfway through, my wife asks me, ‘Are you just venting?’ I said, ‘Yes, lack of expression equals depression.’ So, I’m going through these plays. I’m mad. And she’s listening to me. I’m bringing her into my world and I’m releasing it.’’

A documentary called “Borderline Beast’’ will be released soon.

“I’m excited for this opportunity,’’ said Marshall. “I’m excited to use my celebrity, my fame, whatever you want to call it to be one of the faces of mental health.’’

Shira Springer can be reached at springer@globe.com.