Miller's elevation to the top job is an extremely rare move for a lawyer in the Belgian market.
He joined Dexia's Belgian banking division in 2001 to take on a newly-created in-house role, and has been responsible for the integration of Dexia Bank Belgique and Artesia Banking Corporation.
The general counsel post has now been filled by Olivier Van Herftraeten, who joins from former Belgian retail group GIB, which went into liquidation last year.
Dexia uses firms including Allen & Overy and Clifford Chance in Belgium, with Linklaters also now in with the chance of an extended role. The latter is understood to have a limited relationship, advising on corporate governance, but has worked with Herftraeten in the past.
However, Herftraeten said there are no plans for a review. “It's always important for a group like Dexia to maintain continuity,” he said.