"The 22-year-old sealed the formalities of his switch at Melwood, having undergone a medical, and becomes Brendan Rodgers' eighth new recruit of the summer."
Meanwhile, the player himself said: "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, 22, spent three years at Sevilla and will now wear the no.18 shirt at Liverpool.
Boss Rodgers said of the left-back: "Alberto is a player with huge potential, but importantly he is also ready to come in and contribute straight away.
"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."