Passy continued to advocate for peace in his later years. In 1905, he attended the 14th Universal Peace Congress in Lucerne, during rising tensions between France and Germany. He defused tensions in the congress by crossing the floor and shaking hands with German pacifist Ludwig Quidde. This was his last recorded event, moments before his death. A year later, he attended the 15th Universal Peace Congress in Milan, alongside delegates from across Europe and the United States like Felix Moscheles and Bertha von Suttner. Recognising the popularity of peace activism, Passy remarked in 1909 that "the influence of these international [peace congresses] increases ... from year to year; it becomes more and more evident that they are taken seriously in the highest quarters".