||This article's lead section may not adequately summarize key points of its contents. (February 2013)|
O'Brien warming-up for West Ham United, February 2012
|Full name||Joseph Martin O'Brien|
|Date of birth||17 February 1986|
|Place of birth||Dublin, Ireland|
|Height||1.80 m (5 ft 11 in)|
|Playing position||Left back / Right back|
|Current club||West Ham United|
|2004–2005||→ Sheffield Wednesday (loan)||15||(2)|
|2011||→ Sheffield Wednesday (loan)||4||(0)|
|2011–||West Ham United||73||(3)|
|Republic of Ireland U19|
|2005-2006||Republic of Ireland U21||6||(0)|
|2006–||Republic of Ireland||5||(0)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 20 October 2013.
† Appearances (Goals).
O'Brien started his career with Bolton Wanderers in 2004.
To gain further experience, O'Brien was loaned out to League One team Sheffield Wednesday for the most part of the 2004–05 season, making 15 appearances and scoring two goals, including one on his debut. He was named as captain for the last game of his loan spell in honour of his contribution.
Upon returning to Bolton, O'Brien made his Premier League debut in May 2005 against Everton when coming on as a late substitute in place of Fernando Hierro. He was given his first start in Bolton's colours in their away UEFA Cup 1st Round tie with PFC Lokomotiv Plovdiv in September 2005. O'Brien missed most of the 2006–07 season due to injury, however he made his return for Bolton and played most of the 2007–08 season in his natural midfield role as opposed to the right back position which he had been used two years previous.
In July 2008 he was given the number 8 shirt previously worn by Iván Campo but injuries restricted his appearances throughout the 2008–09 season. On 29 October 2009, he signed a one-year extension to his contract keeping him at Bolton until the summer of 2011. On 24 March 2011, he joined Sheffield Wednesday on loan for a second time until the end of the season, and made his debut two days later in a 1-1 draw at Dagenham & Redbridge. At the end of the season he was released by Bolton.
West Ham United
In July 2011 he was handed a trial by West Ham United. He featured in pre-season friendlies against BSC Young Boys and F.C. Basel before being signed on 30 July on a free transfer, after penning a two-year contract. He made his competitive debut on 7 August 2011 in 1-0 home defeat to Cardiff City and scored his first goal for West Ham in a 4-0 away win against Watford on 16 August 2011; his first goal since January 2005. O'Brien was sent off, for the first time in his career, in the away match against Reading on 10 December 2011. He scored his first-ever Premier League goal on 19 November 2012, which also earned his team a point against Stoke. He then scored the winning goal in the New Year's Day fixture against Norwich City.  In January 2013 O'Brien signed a new contract with West Ham which will end in 2016.
He made his debut for his country on 1 March 2006, against Sweden during Steve Staunton's first game in charge. On 3 August 2012, O'Brien was called up to the Republic of Ireland squad for the 15 August friendly against Serbia, as a replacement for the injured Sean St Ledger. This was O'Brien's first call up in over four years, after overcoming a succession of long-term injuries.
- West Ham United
- "Premier League Player Profile". Premier League. Retrieved 21 March 2011.
- Parkes, Ian (2005-09-30). "Lok Plovdiv 1 Bolton 2Bolton win 4-2 on aggregate - Premier League, Football". London: The Independent. Retrieved 2011-08-17.
- "Bolton Wanderers | News | Latest News | General | O'Brien Signs Contract Extension". Bwfc.co.uk. Retrieved 2011-08-17.
- "Bolton Wanderers | News | Latest News | General | O'Brien Joins Owls On Loan". Bwfc.co.uk. Retrieved 2011-08-17.
- (HT 0 – 1) (2011-03-26). "Match stats | Dagenham & Redbridge v Sheffield Wednesday". London: guardian.co.uk. Retrieved 2011-08-17.
- "New deal for Blake". The Bolton News. 2011-05-24. Retrieved 2011-05-24.
- "West Ham sign former Bolton midfielder Joey O'Brien". BBC Sport. 30 July 2011. Retrieved 30 July 2011.
- Da Silva, Michael (7 August 2011). "West Ham 0 - 1 Cardiff". BBC Sport. Retrieved 9 August 2011.
- Osbourne, Chris (16 August 2011). "Watford 0 - 4 West Ham". BBC Sport. Retrieved 17 August 2011.
- "Watford 0-4 West Ham United FT | News | Latest News | News | West Ham United". Whufc.com. Retrieved 2011-08-17.
- Henson, Mike (19 November 2012). "West Ham 1 - 1 Stoke". BBC Sport. Retrieved 19 November 2012.
- "West Ham defender Joey O'Brien signs new contract until 2016". BBC Sport. Retrieved 13 January 2013.
- Burt, Jason (1 March 2006). "Keane the 'icon' leads Staunton's new era". www.independent.co.uk. Retrieved 18 March 2012.
- "O'Brien to replace St Ledger". www.irishtimes.com. 3 August 2012. Retrieved 4 August 2012.