Throughout his career, McGregor has become the subject of many controversies due to his behaviour, ranging from driving offences to assault, disorderly conduct and rape.

In November 2024, the Irish High Court, in a civil case, found that he assaulted and raped a woman in December 2018, ordering him to pay over €248,000 in damages.

[27] While in Lucan, he met future UFC fighter Tom Egan and they soon started training mixed martial arts (MMA) together.

[29][30] On 17 February 2007, at the age of 18, McGregor made his mixed martial arts debut in an amateur fight against Kieran Campbell for the Irish Ring of Truth promotion in Dublin.

After McGregor won his second fight against Mo Taylor, he made his featherweight debut in a loss via kneebar against submission specialist Artemij Sitenkov.

After a victory at featherweight in his next bout against Stephen Bailey, McGregor contemplated a different career path before his mother contacted his coach John Kavanagh and reinvigorated him to continue pursuing mixed martial arts.

Following this, during 2011 and 2012, McGregor went on an eight-fight winning streak,[33] during which he won both the CWFC Featherweight and Lightweight championships, making him the first European professional mixed martial artist to hold titles in two divisions simultaneously.

[41] McGregor was expected to face Cole Miller on 19 July 2014, at UFC Fight Night 46 in his comeback bout after recovering from his ACL injury.

[73][74][75] Both competitors were awarded "Fight of the Night" bonuses, and McGregor received the highest disclosed purse of any fighter in the history of the company to that point, at $1,000,000.

[87] This result marked the first time a competitor had held UFC championships in two different weight classes, and it also repeated McGregor's feat during his career at Cage Warriors.

[90][91][92] On 26 November, due to his inactivity in the division, it was initially announced that McGregor had vacated the Featherweight Championship, therefore promoting José Aldo to undisputed champion.

[147] On 14 June 2017, it was announced that McGregor would compete in his first professional boxing match against the undefeated Floyd Mayweather Jr., on 26 August 2017 at T-Mobile Arena in Paradise, Nevada.

[155] On 23 November 2023, in response to the stabbing of a woman and three children in Dublin, McGregor made multiple anti-immigration statements, tweeting that "Ireland is at war".

[168] Musgrave delisted McGregor-linked drinks,[169] resulting in SuperValu, Costcutter, Centra and Carry Out ceasing to sell McGregor's Forged Irish Stout and Proper No.

[170] Tesco and Ocado additionally pulled all alcoholic products associated with McGregor from their stores,[171][172] alongside Wetherspoons, Asda, and BWG Group who stopped stocking Proper No.

McGregor told the 46-year-old to "Dance for me, boy," at a promotional event in Los Angeles, before urging the crowd to yell obscenities at Mayweather, his wife and children.

Do not ever put me in a bracket like this again..."[220] On 11 March 2019, McGregor was arrested outside of the Fontainebleau Hotel in Miami Beach, Florida, after he attacked a fan taking a picture with a cellphone.

They attempted to confront Nurmagomedov, who was on a bus leaving the arena with "red corner" fighters for UFC 223 on it, such as Rose Namajunas, Al Iaquinta, Karolina Kowalkiewicz, Ray Borg and Michael Chiesa.

[250] McGregor pleaded no contest to a count of disorderly conduct and was ordered to perform five days of community service and attend anger management classes.

[252] Following the fight at UFC 229 on 6 October 2018, Khabib Nurmagomedov jumped out of the cage and charged towards McGregor's training partner Dillon Danis.

[258] On 15 August 2019, TMZ Sports published a video that showed McGregor punching an older man at The Marble Arch Pub in Dublin.

[275][276] In March 2019, The New York Times reported that McGregor was under investigation by the Garda Síochána (police), following allegations of a sexual assault on a woman in a Dublin hotel in December 2018.

[279] In January 2021, after prosecutors declined to prosecute McGregor for the 2018 alleged sexual assault, a civil claim for damages was launched in the High Court.

[280][281] In March 2022, the High Court made a pre-trial discovery order against McGregor requiring the Gardaí to disclose certain information and documents gathered by them.

[290][291][292] After the trial, McGregor indicated on social media that he planned to appeal the verdict, and Hand said she hoped that the case would encourage victims of assault to continue "pushing forward for justice".

[296] In light of the court ruling, IO Interactive ceased its collaboration with McGregor, removing content that featured him from their Hitman video game series.

[301] On 10 September 2020, McGregor was arrested on the French island of Corsica on suspicion of attempted sexual assault and indecent exposure for an incident alleged to have taken place in a bar.

The plaintiff, identified as a vice president at a prominent Wall Street financial firm, claims that McGregor "intentionally engaged in unlawful sexual contact", "attempted to forcefully place his unprotected penis into [her] mouth without her consent".

Key details of the lawsuit include an allegation that the woman was led to the men's restroom by a member of McGregor's team; and that arena staff and security were aware of potential misconduct but failed to provide adequate protection.

The plaintiff's attorney, Jim Dunn, stated that his client's main goal in filing the lawsuit is to raise awareness and encourage others to report sexual assault.