Newby was Secretary of the Social Democratic Party Parliamentary Committee in 1981, David Owen described him as 'an able young civil servant who resigned to come and work for us', and National Secretary of the SDP from 1983 to 1988. He had parliamentary ambitions seeking the candidacy for Twickenham, challenging Vince Cable, in 1997. From 1999 to 2006, Newby was Chief of Staff to Charles Kennedy. He was instrumental in the process of managing the succession of leadership from Kennedy to Menzies Campbell.