Joseph Martin O'Brien (born 17 February 1986) is a retired Irish professional footballer who played as a full-back and defensive midfielder for Bolton Wanderers, Sheffield Wednesday, West Ham United and Shamrock Rovers.

[2] To gain further experience, O'Brien was loaned out to League One team Sheffield Wednesday for the most part of the 2004–05 season,[3] making 15 appearances and scoring two goals, including one on his debut.

[8] Upon returning to Bolton Wanderers from a loan spell at Sheffield Wednesday, O'Brien made his Premier League debut on 15 May 2005 against Everton when coming on as a late substitute in place of Fernando Hierro.

[12] Initially playing as a centre-midfielder, O'Brien changed to a right-back role and made an impression, leading to Manager Sam Allardyce described him as a "dominant force at right back in the Premiership".

[14] By October, O'Brien was expected to return from a pitch in a months time,[15] with a help from an American doctor Dr Frank Jarrell, a pioneer in the field of spinal reflex analysis.

[17] Having regained his fitness,[18] it wasn't until on 23 September 2007 when he made his return for Bolton, making his first start and playing the whole game, in a 1-0 win over Tottenham Hotspur.

[19] Since making his return from injury, he played most of the 2007–08 season in his natural midfield role as opposed to the right back position which he had been in two years previous.

In July 2008 he was given the number 8 shirt previously worn by Iván Campo and started well when he provided two assists against Stoke City[23] and Arsenal.

[31] On 24 March 2011, O'Brien joined Sheffield Wednesday on loan for a second time until the end of the season,[32] and made his debut two days later in a 1–1 draw at Dagenham & Redbridge.

He featured in pre-season friendlies against BSC Young Boys and Basel before being signed on 30 July on a free transfer, after penning a two-year contract.

[52] In the same match he suffered a dislocated shoulder after he "fell awkwardly following an off-the-ball push from Chelsea defender Gary Cahill" and was sidelined for three months.

[57] After appearing five times in the Europa League matches for West Ham United campaign, he suffered a calf injury at the start of the season.

In February 2006, O'Brien was called up to the Republic of Ireland squad for the first time[68] and made his debut for his country on 1 March 2006,[69] against Sweden during Steve Staunton's first game in charge.