The Reds have been chasing the Spain Under-21 left-back all summer and after agreeing a fee on Tuesday, have finally completed the transfer - their eighth of the transfer window
Brendan Rodgers has courted the Spanish left-back for most of this summer, finally completing the deal on the eve of their Premier League opener for a fee believed to be in the region of £12 million.
As reported by Goal, the Reds went back to the negotiating table at the start of August and were confident that they could strike a deal, before confirming on Tuesday that a fee had been agreed.
And the Spain Under-21 international is delighted to complete his move to Anfield, telling the club's official website: "In my view, Liverpool are the best club in England and I couldn't waste an opportunity to come and play for them.
"I spoke with Xabi Alonso, Pepe Reina and Alvaro Arbeloa and they told me this is a spectacular club whose fans follow it in a very special way.
"They all told me I can grow a lot here as a footballer as this is a massive club. I'm very happy to be joining a club as big as Liverpool. I hope to give my best and do all I can to help."
Moreno becomes Rodgers' eighth signing of the summer as the Northern Irishman continues to build for a season that welcomes Champions League football back to Anfield, and he believes the 22-year-old can make an immediate impact.
"Alberto is a player with huge potential, but importantly he is also ready to come in and contribute straight away," Rodgers said.
"He is quick, strong and serves the ball really well.
"We have monitored him in Spain for some time and every time I have seen him I have been greatly impressed.
"What is also important is that he is hungry to improve and recognises it is vital to keep learning."