Mr Dilnot, an alumnus of Sandhurst and Boston Consulting Group (BCG), joins from high-tech tool firm Danaher, where he has worked since 2005, latterly as group president, emerging markets, of its Gilbarco Veeder-Root subsidiary that serves the petroleum industry and president of Danaher Middle East.
The new chief executive succeeds Tom Drury, who left Shanks in September, and starts on 1 February 2012.
Prior to joining Danaher, Mr Dilnot spent seven years at BCG in London and Chicago, working across a range of industries.
He originally trained as an army helicopter pilot, spent nine years in the service and saw active service with both NATO and the UN. He has a degree in mechanical engineering from Bristol University.
Shanks reported a 14% rise in half-year revenues, to £398m. For the six months to 30 September 2011, pre-tax profit was up 70% to £17.9m and EBITDA up 10% to £53.7m.
Chairman Adrian Auer said: "Shanks is in great shape with good prospects. In Peter we have appointed a top class executive with a most impressive track record. I have no doubt Peter will bring the energy and leadership to maintain the momentum of our progress to date and manage the next phase of Shanks' growth."