The Belgian international completed his move to Reds from Sunderland on Tuesday, and expressed his gratitude to the Black Cats and their fans for the support he received during his three years on Wearside.
Mignolet wrote on Twitter: "Delighted, very proud and privileged to be the first Belgian signing for such a big club @LFC #YNWA Many thanks for all the reactions!
"Also want to thank @SAFCofficial for the three amazing years I had in Sunderland.
"I will never forget the support I received from all of you. Especially the safc supporters!!!"
Mignolet played in every single Premier League game for Sunderland last season.