The England international, who has made 70 appearances for the Reds, committed his future to the club by signing the deal at Melwood.
Liverpool FC Director of Football Damien Comolli said: "We are absolutely delighted. We were in talks for a few weeks, but it was easy to find an agreement because he wanted to stay and we wanted him to stay.
"We are very pleased he wants to commit long term, and I think he was pleased we went to him and asked him to commit long term.
"His best years are to come. Very often defenders peak between 26 and 31, so he is just entering into those years where a maturity comes in and his knowledge of the game gets better and better. We are happy his long-term future is at Liverpool."
Johnson joined Liverpool two years ago from Portsmouth and marked his Anfield debut with a spectacular goal in a 4-0 victory over Stoke City in August 2009.
The 26-year-old tallied 35 appearances overall during his first season with the Reds - a figure he matched last term as he showcased his versatility by operating on both the right and left side of defence under Kenny Dalglish.
Comolli added: "It's obvious when you watch him play his technical ability is second to none. Physically he is absolutely fantastic as well and his fitness level is great.
"Towards the end of last season he showed how versatile he is by playing at left-back or right-back - mostly at left-back - and was outstanding.
"For us he is a great asset to have around. As we've always said, we don't want to sell our best players or sell our assets and as long as the players are happy to be here, we're happy to commit to them."
Liverpool FC Director of Football Damien Comolli said: "We are absolutely delighted. We were in talks for a few weeks, but it was easy to find an agreement because he wanted to stay and we wanted him to stay.
"We are very pleased he wants to commit long term, and I think he was pleased we went to him and asked him to commit long term.
"His best years are to come. Very often defenders peak between 26 and 31, so he is just entering into those years where a maturity comes in and his knowledge of the game gets better and better. We are happy his long-term future is at Liverpool."
Johnson joined Liverpool two years ago from Portsmouth and marked his Anfield debut with a spectacular goal in a 4-0 victory over Stoke City in August 2009.
The 26-year-old tallied 35 appearances overall during his first season with the Reds - a figure he matched last term as he showcased his versatility by operating on both the right and left side of defence under Kenny Dalglish.
Comolli added: "It's obvious when you watch him play his technical ability is second to none. Physically he is absolutely fantastic as well and his fitness level is great.
"Towards the end of last season he showed how versatile he is by playing at left-back or right-back - mostly at left-back - and was outstanding.
"For us he is a great asset to have around. As we've always said, we don't want to sell our best players or sell our assets and as long as the players are happy to be here, we're happy to commit to them."
