When Campbell takes control of the legal function deputy group secretary Aileen Taylor will take on the group secretary role.
The move was announced to the Stock Exchange this morning as the bank reported a £3.6bn loss for the 2009 calendar year.
McLean, who has spent almost 40 years at RBS, is stepping down at the same time as RBS deputy chief executive Gordon Pell.
McLean has held the position of group general counsel and group secretary since 2003, having joined the bank as a graduate trainee in 1970 and becoming a member of the organisation’s executive a decade later.
Campbell joined RBS from Dundas & Wilson in 2005, having been managing partner of the Edinburgh-headquartered firm since 1996 (31 May 2005).
No one at RBS was available for comment, but chairman Philip Hampton said in a statement: “I’m extremely grateful to Miller for his dedication, loyalty and outstanding contribution to the group over a long and distinguished career spanning nearly 40 years. He’s played a critical role over the years and we wish him a long and very happy retirement.”