King was an adventurous mountaineer. He was the first to reach the summits of Mont Maudit with William Edward Davidson and guides Johann Jaun d. J. and Johann von Bergen on 12 September 1878, and Aiguille Blanche de Peuterey (Pointe Güssfeldt) with guides Emile Rey, Ambros Supersaxo and Aloys Anthamatten on 31 July 1885. The SE summit of the Aiguille Blanche de Peuterey () is named Point Seymour King in his honour.