Jackson made a surprise debut as the starting outhalf against Scarlets in February 2011. The young playmaker had represented Ireland at a number of levels and was included in the Ireland Junior World Championship squad in 2011. Jackson primarily played at fly-half but can also play at inside centre. Jackson played arguably his best game against Connacht Rugby in 2012 when he scored a try, a conversion, and three penalties. He earned his place in the Ulster starting lineup including the defeat to Leinster Rugby and then the Heineken Cup 22-19 win over Edinburgh Rugby. In 2014, Jackson and some teammates found themselves the subject of some controversy when a social media posting by Jackson came to light of them at a party, blacked-up, in slave costumes and holding an Ethiopian flag. Ulster Rugby apologised "unreservedly for any offence" and Jackson removed the post. The Irish Rugby Football Union were also involved in the handling of this incident.
On 14 April 2018, the Irish Rugby Football Union revoked Jackson's Ulster and Ireland contracts following his rape trial and acquittal.
Perpignan
Following his banishment from Irish rugby, Jackson signed a two-year contract in June 2018 with Perpignan in France.
London Irish
Jackson exercised a clause in his contract with Perpignan that allowed him to leave the club when they were relegated from the Top 14. He signed with London Irish, who had been guided back to the English Premiership for the 2019–20 season by former Ireland head coachDeclan Kidney. Before the start of the season, London Irish sponsor, Cash Converters, announced that they were withdrawing sponsorship of the club, and many fans also tweeted that they would boycott the club, using the #IBelieveHer hashtag. This was followed six days later by an announcement by Diageo that they would be withdrawing their Guinness-branded sponsorship from the club as a result of Jackson's signing. They said in a statement "We have met with the club to express our concerns. Their recent decision is not consistent with our values and so we have ended our sponsorship." Diageo and Guinness had sponsored the club for the previous 27 years.
Jackson, along with Stuart Olding, Blane McIlroy, and Rory Harrison, was arrested and questioned about allegations of a rape and sexual assault alleged to have taken place during an after-party at Jackson's home in South Belfast in the early hours of 28 June 2016. In July 2017, they were told by the police that they would face charges in relation to the alleged rape and sexual assault. The trial started in January 2018, with prosecution and defence concluding their cases in late March. On 28 March 2018, after less than 4 hours of deliberation, the jury delivered a unanimous not guilty verdict for all four men. Following the trial and the release of text messages sent to a WhatsApp group, a series of protests and condemnation was levelled at Jackson for leaving the complainant in a distressed way and the sexist and degrading tone of the messages. On 6 April 2018, Jackson acknowledged that the condemnation was "fully justified" and apologised adding "I am also truly sorry for engaging in a WhatsApp group chat which was degrading and offensive and I apologise unreservedly for this." In March 2018, Jackson's solicitors announced that he intended to sue Irish Labour Party Senator Aodhán Ó Riordáin for defamation following a tweet Ó Riordáin made following Jackson's acquittal. Jackson's and Olding's contracts were revoked by Ulster Rugby and the IRFU on 14 April 2018, following a review. A statement from the IRFU stated "In arriving at this decision, the Irish Rugby Football Union and Ulster Rugby acknowledge our responsibility and commitment to the core values of the game: Respect, Inclusivity and Integrity. It has been agreed, as part of this commitment, to conduct an in-depth review of existing structures and educational programmes, within the game in Ireland, to ensure the importance of these core values is clearly understood, supported and practised at every level of the game." Jackson released a statement, saying "I am deeply disappointed about the outcome of the IRFU and Ulster Rugby's internal review. However, I recognise that my behaviour has fallen far short of the values expected of me as an international player, a role model for the game of rugby and as a son and a brother. I am truly sorry."
