Complex sentence: Before this, he worked with Carroll Winter & Co Chartered Accountants from 1959 to 1960, and then with Peat Marwick Mitchell & Co from 1960; he was a partner with them from 1973 to 1979.
Split into simpler sentences: Before this, he worked with Carroll Winter & Co Chartered Accountants from 1959 to 1960 and then with Peat Marwick Mitchell & Co in 1960. He was a partner with them from 1973 to 1979.