Alan Rusbridger said he would take over as chairman of The Scott Trust, which owns Guardian Media Group and was created to safeguard its journalistic freedom.
Rusbridger's leadership saw the paper expand from a Britain-only newspaper to an international media organisation with a strong web presence.
Rusbridger made headlines last year when he defended the newspaper's publication of files leaked by ex-National Security Agency contractor Edward Snowden, saying its coverage has prompted a debate about the extent of intelligence activities and exposed the limits of regulatory laws.