Capital punishment was abolished in Slovenia in 1989, when it was still a federal republic of the former Yugoslavia. When Slovenia introduced its democratic constitution on the 23 December 1991 capital punishment became unconstitutional.
The last execution was a hanging which took place in 1957.
Article 17 (Inviolability of Human Life)
Human life is inviolable. There is no capital punishment in Slovenia.
On 1 July 1994 protocol No. 6 to the ECHR came into force. Later Slovenia also adopted the Second Optional Protocol to the ICCPR.
References
Capital punishment in Slovenia Wikipedia(Text) CC BY-SA