Under the modified instant-runoff voting system employed for the election , only the votes cast for Livingstone and Norris were considered in the second round , where Livingstone won with 58 % of first - and second-preference votes , versus 42 % for Norris . Under the supplementary voting system employed for the election , only the votes cast for Livingstone and Norris were considered in the second round , where Livingstone won with 58 % of first - and second-preference votes , versus 42 % for Norris .