Newton was first elected for the new constituency of Braintree in February 1974 with a majority of 2,001, and successfully retained the seat in the October 1974 general election with a reduced majority of 1,090. The Conservative victory at the 1979 general election boosted his majority dramatically to 12,518, and it increased at every subsequent election to a high of 17,494 at the 1992 general election before his defeat in the Labour landslide at the 1997 general election by 1,451 votes.
In the 1997 Prime Minister's Resignation Honours, after Newton lost his seat, he was raised to the peerage as Baron Newton of Braintree, of Coggeshall in the County of Essex on 31 October 1997. He attempted to be selected for the 1999 European Parliament Election, but was unsuccessful. In 1998 he was appointed a professional standards director of the Institute of Directors. A position he held until 2004. Newton chaired the Hansard SocietyCommission on Parliamentary Scrutiny which ran from 1999 to 2001. The Commission concluded that Parliament was being left behind by changes in the constitution, government and society and set out reforms for improving its function. On 1 November 2007 he was appointed the first chairman of the new Administrative Justice and Tribunals Council. He became a chairman of the Further Education Funding Council for East Region, serving between 1998 and 2001, the privy councillors' committee on the Anti-Terrorism, Crime and Security Act 2001 between 2002–2004, the Tax Law Rewrite Steering Committee between 2007 2007 and 2010), the North East Essex Mental Health NHS Trust between 1997 and 2001, the Royal Brompton and Harefield NHS Trust between 2001 and 2009, East Anglia's Children's Hospices between 1998 and 2002 and Help the Hospices between 2002 and 2010. He became a deputy lieutenant of Essex in 2002
Personal life
Newton was married to Janet Huxley from 25 August 1962 until they divorced in 1986. He married Patricia Gilthorpe née Thomson on 26 September 1986. Her first husband had died. Among the many tasks he took on were the chairmanships of the Further Education Funding Council for East Region ; the Council on Tribunals, later the Administrative Justice and Tribunals Council ; the privy councillors' committee on the Anti-Terrorism, Crime and Security Act 2001 ; the Tax Law Rewrite Steering Committee ; the Standing Conference on Drug Abuse ; the North East Essex Mental Health NHS Trust ; the Royal Brompton and Harefield NHS Trust ; the Hansard Society Commission on Parliamentary Scrutiny ; East Anglia's Children's Hospices ; and Help the Hospices. He was the professional standards director of the Institute of Directors and became a deputy lieutenant of Essex in 2002. Newton was a heavy smoker from an early age. He died at Colchester Hospital of chronic obstructive pulmonary disease on 25 March 2012. He was survived by his two daughters from his first marriage.