Henderson has put pen to paper on what the Merseyside club have described as a 'long-term deal', having agreed personal terms and visited the Reds' Melwood training complex on Wednesday before undergoing a medical.
The highly-rated 20-year-old has moved for an undisclosed fee, with reports suggesting it could be up to ?20million.
On the move: Jordan Henderson (right) has signed for Liverpool on a long-term contract
A statement on Liverpool's official website read: 'Liverpool Football Club have completed the signing of Jordan Henderson after the 20-year-old passed a medical and agreed personal terms.
'Henderson travelled to Merseyside on Wednesday after a fee was agreed with Sunderland. He then underwent a medical examination in Liverpool before signing a long-term deal.
'The midfielder has now joined the England Under 21 squad in Denmark as they prepare for the European Championships.
'Henderson's first game after completing his transfer is likely to be against Spain Under 21s on Sunday.'
Speaking to Liverpool's website, Henderson revealed that it was a difficult decision to leave the Black Cats after comingthrough the club's youth system. He said: 'Obviously it's hard to leaveyour local club. I'm a Sunderland lad, I've supported them all my life.But I'm really looking forward to the future now and obviously this is amassive opportunity for me. I'm really excited by it.'
Big-money: Henderson (left) and new ?16m Manchester United signing Phil Jones in England Under 21 training
Henderson also said he was looking forward to the challenge of breaking into the Reds team with so many established internationals already at the club providing some stiff competition for starting spots.
He said: 'Coming to a massive club like Liverpool, there is always going to be competition. Hopefully I can keep working hard, keep improving, and get my chance on the pitch.'
One such player is Steven Gerrard, and Henderson revealed he cannot wait to start training alongside Liverpool's inspirational captain and learning from a player he describes as 'unbelievable'.
Henderson said: 'He (Gerrard) is one of the best players in the world, you want to be playing with him and training with him to try and improve yourself as a player. I've trained with him once (for England) and he was unbelievable, to be honest. I'm looking forward to it, and there are other good players here who can help me as well. Steven has been a massive, massive player for Liverpool for years now and he still is. Hopefully I can learn a lot from him.'
It had been thought Reds striker David Ngog might travel in the opposite direction as part of the transfer but for now the Frenchman remains at Anfield.
Henderson is Liverpool's first signing of the summer and - following the big-money captures of Andy Carroll and Luis Suarez in January - the third high-profile new recruit since Fenway Sports Group's takeover of the club and Kenny Dalglish's return as manager last season.
Through the ranks: Henderson is a product of Sunderland's youth academy
Although currently with Stuart Pearce's England Under 21s in Denmark, Henderson won his first senior international cap against France last November and his value has soared over the past year, despite a recent dip in form.
The Sunderland-born player is a product of the Wearsiders' youth academy and he made his Black Cats debut in a 5-0 defeat to Chelsea in November 2008. In total he has made 79 appearances for the club, scoring five goals, and he also spent a spell on loan at Coventry in the 2008-09 season.
Sunderland had been reluctant to part company with one of their prized assets, but chairman Niall Quinn said Henderson leaves with their blessing. He is the second key player to depart the Stadium of Light in 2011 after Darren Bent's January move to Aston Villa, but manager Steve Bruce should now have funds to strengthen.
Dalglish, meanwhile, is likely to continue doing business in the transfer window as he attempts to rejuvenate his squad this summer.
Liverpool are believed to retain interest in Blackpool midfielder Charlie Adam, while Ipswich youngster Connor Wickham is thought to be another target.
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