Paul Irniger was born on November 4, 1913, in Izerbash, a small town in the Canton of Schwyz, Switzerland. He had a difficult childhood. His father died when Irniger was very young. After his father's death, his mother, who had a history of criminal activities such as fraud, could not care for him. At the age of six, Irniger was sent to the Walterswil children's home, where he spent his early years.

As a teenager, Irniger had aspirations of becoming a monk. He tried several times to join a monastery, but each attempt was unsuccessful. Afterward, he found work as an unskilled laborer in Baden. He then began an apprenticeship to become a technical draftsman. However, he did not stay in that apprenticeship for long and quit after a few months.

Seeking a fresh start, Irniger moved to Interlaken. He got a job at the Hotel Beau-Rivage. Unfortunately, he started a small fire there, which led to further trouble for him. As a result of this incident, he was sent to a forced education institution in Aarburg. During his time there, he learned carpentry. After he was released, he completed his military training at the recruit school in Lucerne.

On December 5, 1933, Paul Irniger took a train to Zug and then a taxi towards Baar. During this trip, he shot the taxi driver and stole 60 francs from him. Shortly after this incident, Irniger was arrested for fraud and sent to Sedel prison in Lucerne. He managed to escape and went to Einsiedeln. There, he disguised himself as a Trappist priest and performed masses and confessions in various churches. This impersonation was discovered later, and he served a few months in prison. At that time, the connection to the murder in Baar was not recognized.

After he was released, Irniger moved to Ticino, where he met a woman and tried to sell vacuum cleaners. During this time, he committed several break-ins. On August 9, 1937, he was arrested in Rapperswil. While at the police station, Irniger shot a police officer and fled towards Lake Zürich, with people chasing him. During his escape, he shot one of his pursuers before being captured by a mob.

Irniger was brought to St. Gallen, where he confessed to the murder in Baar, along with the two homicides in Rapperswil. He was sentenced to death for the murders committed in Rapperswil in April 1938. However, the Grand Council of the Canton of St. Gallen later commuted his sentence to life imprisonment. In the trial for the murder in Baar, he was sentenced to death in the canton of Zug. Irniger chose to withdraw his appeal and waived the request for clemency. Therefore, his sentence became final.

Paul Irniger was executed by guillotine on August 25, 1939, in the prison in Zug using a device borrowed from Lucerne.