Industry sources said he would be leaving next month. One said: "It is getting about that Gus is resigning. It's his decision."
Roche joined the group after O'Rourke had bought Laing Construction for £1. He was confirmed as group procurement director when the Laing O'Rourke board was announced last year.
Roche's decision to leave follows the departure of Peter Stone, Laing O'Rourke's commercial director, this month. Stone had been the last survivor from Laing remaining on the board.
The group was also hit by the departure of former chief operating officer Andy White last September. White left after five months in the post – he was formerly at rival contractor Alfred McAlpine.
Laing O'Rourke refused to comment.