West Ham United are delighted to confirm the signing of Republic of Ireland international Joey O'Brien.

The 25-year-old joins the Hammers on a free transfer following his release by Bolton Wanderers earlier this summer.

Capped three times by his country, Dublin-born O'Brien has been with West Ham since the club began pre-season training four weeks ago. He travelled with Sam Allardyce's squad to their pre-season training camp in Switzerland and has featured in matches against BSC Young Boys, FC Basel, FC Copenhagen, Wycombe Wanderers and Dagenham & Redbridge.

"Obviously I'm delighted to finally sign because I've been here since the start of pre-season," said a smiling O'Brien. "It's been a few weeks now and it's gone well. The manager wanted me to sign and as soon as I heard that, there was no real hesitation.

"I'm pleased it's done and dusted."

A precocious talent as a teenager, O'Brien joined at the age of 16 in 2002, making his first-team debut under Allardyce in a Carling Cup tie against Yeovil Town in September 2004.

After a successful loan spell at Sheffield Wednesday, he returned to the Reebok Stadium to make his Premier League debut in May 2005 and his first start in a UEFA Cup tie with PFC Lokomotiv Plovdiv in September of the same year.

O'Brien's form saw him secure a call-up to the senior Republic of Ireland squad, with a debut arriving in a 3-0 home friendly victory over Sweden in March 2006.

Although injury issues restricted O'Brien's appearances over the next few seasons, he signed a contract extension in 2009 before enjoying a second loan spell at Sheffield Wednesday earlier this year.

Allardyce knows the player well and is convinced that his injury problems are now behind him and that he can play a big part in the Hammers' quest for promotion from the npower Championship this season.

O'Brien becomes West Ham's fourth new signing of the summer, following Abdoulaye Faye, Kevin Nolan and Matt Taylor to the Boleyn Ground.