Kretschmann is born to Catholic parents. He went to school in Riedlingen (District of Biberach). His parents wanted him to become a priest. Instead he joined a school for teaching education and became teacher for Biology, Chemistry and Ethics.
Kretschmann started his political career at the Communist League of West Germany in 1973. He later changed his view and is now part of the more conservative Green party.
In 1979/80 he was a co-founder of the Green Party in Baden-Württemberg. He was leader of the Green Party in Baden-Württemberg from 1983 to 1984 and 2002 to 2011. In 2011 he became ninth Minister-President of Baden-Württemberg. He was President of the Bundesrat from 2012 to 2013.
In the parliamentarian of the Baden-Wuerttemberg state parliament election 2016 he was reelected.
Kretschmann is married and has three children.