[1] During his tenure as archbishop he was a highly divisive figure, who gained strong support from some and drew heavy criticism from others, and he oversaw the separation of church and state in Sweden on 1 January 2000.

In 1992, he became bishop and head of the diocese, and in 1997 he was appointed Archbishop by the Social Democrat-controlled Government of Sweden under the state church which was then still formally in place but lost its true standing already in 1958 and was on its way to be officially abolished.

"I do not have the truth, I seek it" (Jag har inte sanningen, jag söker den) - K. G. Hammar As the head of the church, he gained much popularity as well as criticism for his strong opinions, which emphasized humanism and tolerance according to his supporters, and was highly politically partisan and inappropriate for his position according to his critics, who saw him more as a left wing politician than a clergyman.

He fought for extended amnesty for refugees and illegal immigrants in Sweden, debt relief for poor countries, more humane treatment of prisoners and tolerance towards followers of other religions than Christianity.

[3] The former leader of the Swedish Christian Democrat party Alf Svensson has called Hammar a "leftist populist"[2] and the then-party leader of the Moderate Party Bo Lundgren called on Hammar to either stop using his post as a political platform or to resign and stand for election as a leftist politician instead.

Hammar's theological position lies within a tradition of Christian mysticism and he has on several occasions expressed his gratitude to the writings of former U.N. Secretary-General Dag Hammarskjöld and his book Markings, and also to the Swedish poet laureate Tomas Tranströmer.