Complex sentence: He retained the seat at the 1946 election on an increased two-party vote of 51.8 percent before being defeated at the 1949 election from a 9.3 percent two-party swing.
Split into simpler sentences: He retained the seat at the 1946 election on an increased two-party vote of 51.8 percent. Labor lost Boothby from a 9.3 percent two-party swing.