The defender also explains that Mark Hughes' vision for Stoke City was what convinced him to sign.
The defender departed Brendan Rodgers’ side at the end of last season after the club failed to offer him a new contract ahead of next season.
For a period it seemed he would be heading to Turkey for his next club, but Stoke then moved quickly to secure the 30-year-old, who immediately joined them for their pre-season games in Singapore in the Barclays Asia Trophy.
And he says he knew that he would be leaving Anfield for a long time despite having made 19 appearances for the side last season.
“I knew a long time ago that I would be free in the summer,” stokecityfc.com reports him as saying.
“I was in a very good position and I feel I have made the most of it by coming to Stoke. It wasn’t on the radar to begin with, but things moved very quickly and I’m having a good time now I’ve acclimatised with everybody,”
Mark Hughes sold Stoke City
The defender also says that manager Mark Hughes was a big part of his move as he sold the club and his plans to the player.
The Welsh boss clearly has big ambitions for his side having enjoyed a solid two years in charge so far, with him having transformed the club from the long ball football they were known for into a more footballing side.
And Johnson says he is excited by the new challenge that awaits him at the Britannia.
“The manager really sold the club to me,” he added.
“I met up with him and he really had a lot of good things to say in terms of where the Club is going, what the team are doing and what his targets were. Those targets fitted with me and that’s why I am excited to join here, it could really work well for us and that’s why I accepted this new challenge.”