Nish joined the company in 1997 as deputy finance director and has been heavily involved ScottishPower's merger with PacifiCorp which was completed at the end of last month.
Chairman Murray Stewart said: 'David Nish is an accomplished finance professional with signficant public sector experience gained in the UK and North America.
'We welcome him to the board.'
Both Nish and Russell are members of the Scots ICA.
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