ISG chairman David King paid tribute to Millar, saying he had made a major contribution to establishing the firm and his retirement was well deserved.
Millar's retirement came as the group posted strong half-year results on Tuesday, increasing pre-tax profit by just less than £600,000 to £3.4m for six months to 31 December 2003. Turnover increased £7m to £205m.
King said the firm was in a stronger position than last year, which he described as the firm's "most difficult year yet".
He said the firm had switched to fit-out work valued between £5m and £20m, instead of projects worth more than £20m, which have been thinner on the ground.
Chairman David King said Millar made a major contribution
This market is helping the firm to tick over while it waits for more substantial projects to get going.
King also pointed to opportunities in the PFI market and said the firm was waiting for decisions on three bids worth more than £150m.
King said the firm's facilities management arm Occupancy made a small profit of £97,000 after a restructuring last year and was well placed to increase its market share.