Whilst playing amateur rugby in the All-Ireland League for Dublin University, Osborne was recommended to Leinster during their 2019–20 pre-season training by Noel McNamara, an elite player development officer with the province, and Tony Smeeth, one of the coaches at Dublin University.
[1] Following these two appearances, and his performances for Leinster A in the 2019–20 Celtic Cup and for Dublin University in the All-Ireland League, Osborne was awarded a professional contract with the province for the remainder of the 2019–20 season.
In his first senior start for the province, Osborne played 65 minutes, helping his team to a 13–6 win in Thomond Park.
[2] Osborne joined Munster on a one-year contract for the 2021–22 season,[3] and made his competitive debut for the province as a replacement for Craig Casey in their 42–17 win against the Sharks on 25 September 2021, in what was the provinces opening 2021–22 United Rugby Championship fixture.
[4] Osborne was forced to retire from rugby at the end of the 2021–22 season on medical grounds due to concussion.