He’d had a few brushes with law enforcement, shoving an undercover officer who tried to arrest his friend for being underage in a bar a few years earlier.
But at the age of 28, Zimmerman had set his sights on enforcing the law as a sworn officer rather than breaking it.
While on patrol as a neighbourhood watch coordinator at the Retreat at Twin Lakes gated community in Sanford, Florida, on 26 February, the 28-year-old shot and killed Trayvon Martin, an unarmed 17-year-old schoolboy.
Zimmerman argued that he had acted in self-defence and argued he was within his rights to fire under the “stand your ground” law, and was acquitted of second-degree murder and manslaughter charges in 2013.
The verdict sparked a national outpouring of grief and rage that directly led to the formation of the Black Lives Matter movement.
In the months following his acquittal, Zimmerman was repeatedly in trouble with authorities.
He was detained for allegedly threatening his wife with a gun, arrested on domestic violence charges that were later dropped, and stopped for speeding in 2013.
He said at one appearance that he had $150 to his name and was $2.5m in debt.
He became paranoid about the intensive media coverage and of vigilante reprisals, his brother Robert Zimmerman Jr has said, and was heavily armed everywhere he went.
In a 2014 interview with GQ Magazine, Mr Zimmerman’s brother Robert Jr said the three Zimmerman siblings and their parents Robert Sr and Gladys stayed in hotels for months after the shooting, adopted codenames, had “go-bags” prepared so they could disappear at a moment’s notice, and bought guns. Lots of them.
Desperate attempts to cash-in on his infamy followed, but it seemed his overtly provocative posturing proved a difficult to market.
A planned celebrity boxing fight with the late rapped DMX was cancelled.
In 2014, he turned his hand to art, selling an 18-by-24-inch canvas featuring a blue, waving American flag with the words, “God, one nation, with liberty and justice for all” emblazoned across it for $100,099.
His next piece, an illustration of prosecutor and Florida State Attorney Angela Corey, hit legal trouble when the Associated Press asserted copyright over use of the image.
Zimmerman also faced a three-year investigation by the Department of Justice for infringing Trayvon Martin’s civil rights.
In a video released by his attorneys soon after the case was dropped, he blamed “Barack Hussein Obama” for inflaming racial tensions by saying in a White House speech that if he had a son, that child would look like Trayvon.
“I’m also my parent’s child, and my life matters as well,” Zimmerman said.
“(Obama) by far overstretched, overreached, even broke the law in certain aspects to where you have an innocent American being prosecuted by the federal government.”
In Zimmerman’s telling, he was the true victim. He was broke, unemployable and homeless, his brother Robert Jr said.
Rather than shy away from the spotlight and try to rebuild his life, Zimmerman appeared to stoke the very same racial tensions that he had accused the former president of whipping up.
In October 2015, Zimmerman retweeted a photo which allegedly showed a picture of Trayvon’s deceased body. The original tweet also included the caption, “Z-man is a one-man army”.
He later claimed he was unaware of the image of Trayvon’s body.
In other Twitter posts he used racist stereotypes to call Mr Obama an “ignorant baboon”, insulted Mike Brown, the teenager shot and killed by Ferguson police in 2014, and taunted those who challenged him.
“We all know how it ended for the last moron that hit me. Give it a whirl cupcake,” Zimmerman said to one person.
His Twitter account, which featured a Confederate flag as its profile picture, was suspended soon after he posted semi-nude photos of his ex-girlfriend with her email address and telephone number.
In late 2015, he was arrested again on charges of aggravated assault for throwing a wine bottle at his then-girlfriend, which was later dropped.
In 2016, Zimmerman provoked condemnation when he put up the gun he used to kill Trayvon Martin for auction.
Calling the weapon an “American firearm icon”, he said he intended to use the proceeds to fight the BLM movement and “Hillary Clinton's anti-firearm rhetoric”.
The Gunbroker website originally due to host the auction took it down amid a backlash, and it was shifted to an alternative site United Gun Group. Zimmerman reportedly accepted a bid of $138,900.
Zimmerman was rarely out of the headlines, with his next scrape with publicity coming when he was kicked off dating apps Tinder and Bumble after he was outed using a fake name of “Carter”.
In his defunct profile he described himself as a carefree self-employed consultant, who enjoyed hiking, fishing and preferred to avoid “large crowds”.
He threatened to “beat” Jay Z and feed him to an alligator over what he claimed was harassment of his parents by a documentary crew funded by the superstar rapper.
Then in 2019, Zimmerman suddenly announced he was suing Trayvon Martin’s family, prosecutors and state attorneys for $100m alleging they had conspired to frame him of murder.
The principle claim in the suit was that Rachel Jenteal, who testified at his trial, had posed as Trayvon’s girlfriend and delivered bogus testimony.
The Martin family dismissed the lawsuit as a “shameless attempt to profit off the lives and grief of others” in a statement released soon afterwards.
Zimmerman’s lawyer Larry Klayman, who founded Freedom Watch and has previously filed lawsuits pushing the Obama “Birther” conspiracy, did not respond to requests for comment.
In 2020, Zimmerman filed a defamation lawsuit against Pete Buttigieg and Elizabeth Warren for tweets they sent recognising what would have been Trayvon’s 25th birthday while campaigning for the Democratic presidential nomination.