Richard Cuthbert, chief executive of Mouchel Group, has tendered his resignation with immediate effect.
Mouchel, which has an office in Liverpool, said Cuthbert will work with the group for a short period "to ensure an orderly handover".
Bo Lerenius will become executive chairman until a new chief executive is appointed. The board said it will make a further announcement as appropriate.
Lerenius said: "I would like to express the Board's gratitude to Rich for his many years of service and his continuing belief in and commitment to the business. The Board will focus on maintaining Mouchel's position in its core markets in the interests of all its stakeholders."
Cuthbert led Mouchel's battle against take-over bids from both Interserve and Costain in 2010.
At the time, Cuthbert argued that the company was performing well to overcome its financial problems and would provide long term shareholder value.
On 15 June this year, the group reported that it expected a significant one-off profit on one of its long-term contracts to offset lower profitability than originally expected following commercial conclusions on a number of contracts.
Mouchel added on Thursday that the group was very recently informed that, as a result of an actuarial error, the one-off gain will be £4.3m lower than previously expected which has an immediate and corresponding impact on the profits the group will report for the year to 31 July 2011.
Rod Harris, the new finance director who joined from Carillion Business Services, has reviewed contract risks and project claims, taking into account the continuing challenging business environment.
As a result, the group said it "has decided to increase provisions in respect of these contract risks and project claims by a similar amount to the reduction in the one-off gain".