The Great Mage of the Hero’s Party Reincarnates is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The Battle Against an Arch-Nemesis, Resumed After 300 YearsAt age 13, the genius wizard Rin embarked on a journey with Lista and the hero party to defeat the great evil known as “the Abyss,” which sought to plunge the world into chaos. But as the battle grew more intense, Rin’s body succumbed to the dark poison of the Abyss, putting his life in grave danger.With the words “I’ll come back,” Rin’s soul entered a forced dormancy, only to reawaken 300 years later as a noble boy. Starting his second life in a peaceful world, Rin discovers that on one side of the world, the destined forces of darkness are beginning to stir once more