Complex sentence: He was first elected to the colonial assembly in 1837 and initially served on the compact government (the Tory clique that ruled the colony) from 1848 to 1850 before becoming leader of the opposition and then Premier and Attorney-General in 1854.
Split into simpler sentences: He was first elected to the colonial assembly in 1837, serving from 1848 to 1850. Fisher would become leader of the opposition and then Premier and Attorney-General in 1854.