Complex sentence: In 1823 he permanently entered public life and made the acquaintance of Count Stephen Széchenyi whose companion he was on a long educational foreign tour, on his return from which he became one of the leaders of the liberal movement in the Upper House.
Split into simpler sentences: In 1823 he permanently entered public life and made the acquaintance of Count Stephen Széchenyi whose companion he was on a long educational foreign tour. On his return from this tour, he became one of the leaders of the liberal movement in the Upper House.