The article discusses one of the secondary functions of the French future analytical form futur antérieur—completion in the past. The aim of the study is to examine how this secondary function appeared and developed in Old French. The study draws on the French epic texts of the eleventh-thirteenth centuries represented in the Ancien français subcorpus of the Frantext corpus. The corresponding corpus-based procedures resulted in creating a research subcorpus that includes 53 cases of the use of futur antérieur to express an action in the past. Comparative analysis of contexts with the meaning in question revealed signs of insufficient grammaticalization of futur antérieur in Old French. It allowed us to make a conclusion that the influence of the Latin possessive structure on the forming meaning of the analytical future created the prerequisites for reconsidering its temporal and aspectual meaning in the past. The conducted analysis confirmed the obligatory for Old French projection of the result of a past action expressed by futur antérieur to the future. Two types of reference to the future that appear on different levels of text organization have been defined.