As part of Jack O Connor's backroom team, in O'Sullivan's first season as selector, they captured the All-Ireland title.

In 2004 O'Sullivan tasted victory for the first time as a footballer when South Kerry qualified for the final of the county senior championship.

After the sixty minutes South Kerry retained their title and O'Sullivan picked up a second county winners' medal.

South Kerry ran out one point winners on a score line of 1–08 to 0-10 giving Sullivan a fourth county championship medal.

In 2004 he helped Dromid Pearses win their first ever South Kerry Senior Football Championship beating St Marys on a scoreline of 0–09 to 0–07 in the final.

O'Sullivan was the winner of the Opel Gaelic Player of the Month award for August,[7] and Kerry went on to claim the All-Ireland title by thrashing Cork 3–13 to 1–9.

[8] Kerry ironically became the first team to win consecutive titles since Cork in 1990 the same day, and O'Sullivan became the first man since Tony Hanahoe in 1977 to lift the Sam Maguire twice as captain.

In the 2008 All Ireland senior football final against Tyrone, O'Sullivan contributed 2 points but famously missed great goal chance 4 minutes from time which would have given Kerry the lead.

After being knocked out of the Munster championship by great rivals Cork, they were on the brink of elimination from the All Ireland series by minnows Sligo.

On a dramatic evening in Tralee, Kerry were saved by heroic performances by O'Sullivan (0-04)and Paul Galvin (0-03) as they scraped through by a single point.

This defeat marked the 1st time in O'Sullivan's inter-county career that Kerry failed to reach the All Ireland semi final.

Afterwards Jack O'Connor resigned as Kerry manager with O'Sullivan's old teammate Eamon Fitzmaurice taking over the reins.

O'Sullivan intended to sit out the entire 2013 national league campaign but after Kerry lost their opening 4 games he returned to help the team's fight against relegation.

He then scored 2 points and set up Colm Cooper for the crucial goal in the final as he claimed a 7th provincial medal.

He returned to score 2 points in Kerry's narrow Munster final win over Clare but aggravated an already troublesome knee injury.

Playing in a more withdrawn "quarterback role" O'Sullivan showed the full range of his playmaking abilities as Kerry ran out 12 winners.

O'Sullivan started the quarter-final win over Galway but was subsequently benched due to his ongoing knee issues.

Their victory over Donegal gave O'Sullivan his 5th All Ireland medal and confirmed his status as one of the greatest players in the history of the game.

Afterwards manager Eamon Fitzmaurice confirmed O'Sullivan would need surgery on both knees over the winter but expressed confidence that he would return in 2015.

[11][12] In a released statement he said "“Today, I would like to announce my retirement from inter-county football, It has been an incredibly difficult decision to arrive at but, after a lot of consideration, I feel now is the right time.