The purpose of the present invention is to provide: a steel material for API 5L X60 to X70 grade highly-deformable line pipes that exhibits superior anti-HIC characteristics in a wet hydrogen sulfide environment having a pH of 5 or more, and that has a low yield ratio even after undergoing a coating process at 300 DEG C or less; a method for manufacturing the steel material; and a welded steel pipe. The steel material for highly-deformable line pipes that exhibits superior strain aging characteristics and anti-HIC characteristics has: a specific composition; a metal structure comprising ferrite, bainite and martensitic islands, the area fraction of said martensitic islands being 0.5 to 5.0%, and the difference in hardness between the ferrite and the bainite being 60 or more in terms of Vickers hardness; and has a uniform elongation of at least 9% and a yield ratio of not more than 90% with regard to pre- and post-strain aging treatment at 300 DEG C or less.