11:38AM BST 12 Aug 2011
Negotiations were concluded swiftly after the 25 year-old travelled from Newcastle to have a medical at the club's Melwood training ground yesterday.
The Spaniard is believed to have cost Liverpool in the region of £6 million.
"This is one of the happiest days of my life," he told liverpoolfc.tv.
"I have come to one of the biggest clubs not just in England, but in the world. I am really, really happy."
Enrique becomes Liverpool's fifth signing of the summer, following Stewart Downing, Charlie Adam, Jordan Henderson and Alexander Doni.