How does jean valjean die in Les Miserables?

He dies of old age. He has lived an extremely long life, taking care of his own family, then spending 19 years in prison, then spending a long time recreating himself in Montreuil-sur-Mer, then raising Cosette. In the book, at Marius's and Cosette's wedding, Valjean finally comes clean about his past. Marius is horrified and steers Cosette away from Valjean. When this occurs, Valjean loses the will to live and takes to his bed. It is only when Marius discovers that Valjean saved his life that he realizes that Valjean is truly a great man. Marius and Cosette rush to Valjean's bedside only to find him weak and dying.

When he does die, Fantine and Eponine take him away to heaven as angels. So the ending is uplifting because he has led a full, honorable life.