Complex sentence: Seymour is a long time member of ACT New Zealand and first became involved in ACT New Zealand as a leader of ACT on Campus, and he first stood for ACT in in Mt Albert against Helen Clark, who was Prime Minister at the time.
Split into simpler sentences: Seymour is a long time member of ACT New Zealand, initially becoming involved in the political party as a leader of ACT on Campus. He first stood for ACT in in Mt Albert against Helen Clark, who was Prime Minister at the time.