This book constitutes the refereed proceedings of the 6th International Workshop on Formal Techniques for Safety-Critical Systems, FTSCS 2018, held in Gold Coast, Australia in November 2018. The 10 revised full papers presented together with an abstract of an invited talk were carefully reviewed and selected from 22 submissions. The papers are organized in topical sections on analysis and verification of Safety-Critical Systems; analysis of timed systems; semantics and analysis methods, and model transformation.