In his subsequent nomadic Football League career, he played for Millwall, Bristol City, Colchester United, AFC Wimbledon, Plymouth Argyle and Grimsby Town.

[5] Osborne embarked on a scholarship at the beginning of the 2004–05 season and progressed sufficiently to be named as a substitute in a youthful squad for a Football League Trophy first round match versus Milton Keynes Dons on 28 September 2004.

[6][7] Osborne remained unused during the 3–0 defeat and was named on the bench on two further occasions, before making his debut on the final day of the 2004–05 regular season versus Hull City.

[17][18][19][20] Though Osborne captained the team on occasion during the 2007–08 and 2008–09 seasons, a lack of confidence meant that he spent periods out of favour with manager Andy Scott, which necessitated spells away on loan at Conference Premier clubs Oxford United and Eastbourne Borough.

[21][22][23][24] Osborne scored the first senior goal of his career in a 1–0 win over Shrewsbury Town on 5 January 2008, when he converted a header from a Ryan Dickson corner.

[27][4] Osborne fully established himself in the team and made a career-high 51 appearances during the 2010–11 season,[30] which featured a run to the 2011 Football League Trophy Final.

[42] Osborne was surplus to requirements during the early months of the 2013–14 season and made just one appearance before departing the club on loan on 31 October 2013,[43][44] which was later extended and turned into a permanent deal on 7 January 2014.

[47] Despite missing almost a month after incurring a suspension for a red card received at the end of November, Osborne regained his place upon his return and joined the club on a two-and-a-half-year contract for an undisclosed fee on 7 January 2014.

[44] After suffering a "horrific injury" to his shin during the 2014–15 pre-season,[49] Osborne returned to fitness in mid-August 2014,[50] but thereafter was entirely out of favour with manager Steve Cotterill and made just three appearances during the club's League One title-winning season,[51][52] though he did receive a promotion medal.

[6] A thigh injury suffered early during the 2016–17 pre-season kept Osborne out until October 2016 and as manager Derek Adams' fourth-choice central defender,[65] he made just two appearances before being released from his contract on 16 January 2017.

[68] Five days later, he made his debut versus Hamilton Academical in the Scottish Cup fourth round and conceded a last-minute penalty, which resulted in a 1–0 defeat.

[79] Prior to the beginning of the 2020–21 season, Osborne was appointed first team coach and defensive strategist at Southern League Premier Division South club Walton Casuals.