Tideway has hired Crossrail finance director Mathew Duncan to be its new chief financial officer.
Mr Duncan will join the £4.2bn London supersewer project later this year after three years working on the £15.4bn Crossrail project.
He will replace current CFO Mark Corben, who is to step down after five years in the post.
Tideway has also recruited former Skanska CEO Mike Putnam as a non-executive director.
Prior to his role at Crossrail, Mr Duncan spent 15 years at Balfour Beatty, including interim CEO and finance director of Balfour Beatty Services.
He is the latest senior Crossrail figure to leave the project as it enters its final stages of construction.
It was revealed last month that HS2 would be bringing in Crossrail chairman Sir Terry Morgan as its new chair to replace the outgoing Sir David Higgins.
Crossrail chief executive Andrew Wolstenholme has also left the organisation to join BAE Systems as its UK group managing director for maritime and land.
Last week the Department for Transport confirmed that Crossrail would need an additional £590m for work to complete on the line. This comprised £290m for Network Rail and a further £300m for Crossrail.
The client said the additional money was needed for the installation and testing of systems on the central section of the line.