Marsh replaces Rod Liddle, who was forced to resign after he let his political leanings be known in a column he wrote in The Guardian newspaper, which poked fun at the people participating in the Countryside Alliance.
Taking on the editorship of 'Today' will see March give up all the other roles he has accumulated in more than 20 years at the BBC.
Marsh began his career at the BBC in 1978 when he joined as a news trainee. After working in Belfast and Birmingham, he joined the 'World at One' team in 1980.
After a short spell at ITN, Marsh returned to the BBC as deputy editor of 'World at One', where he introduced Today presenter James Naughtie to the corporation.
In 1989, Marsh was promoted to editor of early evening news programme 'PM' and, in 1993, he moved to edit 'World at One'. In 1996, he brought the two programmes under his editorship and, in 1998, launched Sunday morning news show 'Broadcasting House'.
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