Hans Erni was born in Lucerne, the third of eight siblings, to a cabin cruiser engineer. He studied art at the Académie Julian in Paris and later in Berlin, and admired artists such as Pablo Picaso and Georges Braque.

He is known for having illustrated postage stamps, his lithographs for the Swiss Red Cross, his participation on the Olympic Committee as well as his activism. His 1939 works and first major public success was a mural titled Switzerland: "Vacation Land of the People" was commissioned and displayed for the national exhibition in Zürich.

The Hans Erni Museum, situated in the grounds of the Swiss Museum of Transport in Lucerne, contains a large collection of artwork, he also designed ceramics and theatre costumes and sets. He did the art for Swiss bank notes, in the 1940s but, after the notes were already printed they were never published, because a member of the State Council of Lucerne criticized that Erni was deemed as a communist. However, Erni was never a member of any political party. In 2004, he was awarded the honorary citizenship of the city of Lucerne. On 10 January 2009 he received the SwissAward for lifetime accomplishment.

In his career, he realized about 300 posters and several murals including the 1980 Salon International de l’automobile, Red Cross, ICC, United Nations and ICAO. He illustrated about 200 books and created 90 postage stamps and 25 medals.