Complex sentence: Before becaming Viceroy, he worked as a merchant in neighbouring Argentina, and then brought to Chile by another irishman in Spain's service, Garland, managing to get the job of General Governor of the colony.
Split into simpler sentences: Before becaming Viceroy, he worked as a merchant in neighbouring Argentina, but was subsequently brought to Chile by another Irishman in Spain's service, Garland. Ambrose managed to get the job of General Governor of the colony.