Klaus Tonner was born in Hamburg in 1947. After studying law in Frankfurt am Main and Berlin, he was a research assistant at the University of Economics and Politics in Hamburg from 1972 to 1994, interrupted by periods as a substitute professor at the universities of Oldenburg, Hanover and Bremen. He received his doctorate from the University of Hamburg in 1980.

In 1991 he habilitated at the University of Bremen. In 1994, he was appointed to the Jean Monnet Chair of Civil Law and European Law at the University of Rostock, which he held until his retirement in 2012. From 2006 to 2012, he was a part-time judge at the Rostock Higher Regional Court.

Klaus Tonner was Chairman of the Hamburg Consumer Advice Center (1993-1997), Vice President of the German Society for Travel Law and is currently Vice President of the International Forum of Tour and Travel Advocates (IFTTA). He is co-editor of the legal journals "Verbraucher und Recht" and "Reiserecht aktuell".

His publications deal with consumer law, in particular travel law. Main book publications: Reiserecht in Europa, 1992; Das Recht des Time-sharing, 1997; Der Reisevertrag, 5th ed. 2007; Vertragsrecht - Kommentar, 2010 (co-editor with Armin Willingmann and Marina Tamm); Verbraucherrecht - Beratungshandbuch, 3rd ed. 2019 (co-editor with Marina Tamm); Schuldrecht: Vertragliche Schuldverhältnisse, 4th ed. 2015; Das neue Schuldrecht - Verbraucherrechtsreform 2014 (co-editor with Tobias Brönneke), Online-Vermittlungsplattformen in der Rechtspraxis, 2018 (co-editor with Peter Rott).