In 1970, Saatchi, with his brother, formed the advertising agency Saatchi and Saatchi. They are credited with a number of successful advertising campaigns, most notably the "Labour isn't working" posters on behalf of the Conservative Party for the 1979 British general election and advertisements for the cigarette brand Silk Cut. Maurice Saatchi served as chairman of the firm which became the world's largest advertising agency. However, a shareholder revolt in 1994 ended the brothers' role in the company, and they founded a new company, M&C Saatchi, the following year. The new company has also been described as a success.
Maurice Saatchi was created a life peer as Baron Saatchi, of Staplefield in the County of West Sussex in 1996. He sits in the House of Lords as a Conservative. Under the leadership of Iain Duncan Smith, Saatchi served as shadow Treasury spokesman in the Lords, forming a close relationship with Michael Howard, who was Shadow Chancellor of the Exchequer. Saatchi argued for the simplification of the tax system and that the poorest eight million people in the United Kingdom should not pay income tax. In June 2014, he suggested that small businesses should pay no corporate tax and that investors in said small businesses should pay no capital gains tax in order to "challenge cartel capitalism."
After Howard became leader of the Conservatives in November 2003, Saatchi was appointed joint chairman of the party with Liam Fox. He had responsibility for running the party campaign for the 2005 general election, after which he stepped down. He published his reflections on the election campaign in a Centre for Policy Studies pamphlet If this is Conservatism, I am a Conservative in a chapter entitled How I Lost the Election. Among his failings listed in the document, Saatchi highlighted the following:
He recommended that future Conservative leaders establish a "moral purpose" as an ideology and future direction for the Party.
He is also chairman of the Finsbury Food Group plc, and is a Governor of the London School of Economics. Saatchi is a trustee of the Museum of Garden History, and also a director of the Centre for Policy Studies. He was also a trustee of the Victoria and Albert Museum from 1988 to 1996.
He is a previous recipient of the St. George’s Society Medal of Honour, an award established in 1996 which recognizes American and British industry leaders for significant contributions in the fields of business, finance and education.
He and his brother founded the Saatchi Shul, an independent Orthodox Jewish synagogue in Maida Vale, London, England, in 1998.
Saatchi's first wife was Gillian Osband, a children's book editor and writer whom he had known since childhood and whom he married in 1972. They divorced in 1984 and that same year he married the novelist Josephine Hart (1942–2011), whom he first met when they worked together at Haymarket Publications in 1967. She died on 2 June 2011.
His country property is a mock Tudor castle called Old Hall in Staplefield, West Sussex, built in 1842. There are sixty acres of parkland and ten acres of flowers, trees and lakes. Maurice Saatchi has a fondness for gardening, laid out the garden on the estate and built a conservatory to house semi-tropical plants. The property was the subject of a display article in Architectural Digest in January 1995.
Maurice Saatchi and his brother Charles were listed at number 366 in the Sunday Times Rich List 2008, with an estimated wealth of £220m in advertising and art. In the Sunday Times Rich List 2009 they were listed at number 438.