Complex sentence: His father, Thomas Meagher (1796--1874), was a wealthy retired merchant, who was twice Mayor of the City, which he also represented in Parliament from August 1847 to March 1857.
Split into simpler sentences: His father, Thomas Meagher (1796--1874), was a wealthy merchant who had retired to enter politics. He was twice elected Mayor of the City, which he also represented in Parliament from August 1847 to March 1857.