Laing O'Rourke has received a £22m contract from the Transport for London (TfL) to remodel Willesden Junction that serves London Overground services.
The contract will run from March for a year, and will include civil engineering, track, overhead line and third rail electrification and signalling upgrades.
Laing O'Rourke will also provide additional sidings at Wembley to accommodate longer, five-car London Overground trains.
TfL said that the extension of the depot will be in a north east direction towards the station and at Wembley former freight sidings will be upgraded to stable passenger trains.
The contract is part of TfL's £320m capacity improvement programme to improve the capacity of London Overground. As part of the programme, TfL is planning to build new storage facilities, upgrade existing maintenance depots, and extend platforms at several stations across the network.
TfL further said that platform works will be carried out at 12 stations on the Highbury & Islington to New Cross, Crystal Palace, West Croydon and Clapham Junction routes and 17 stations on the Richmond to Stratford route.
TfL London Overground director Mike Stubbs said: "This is a key contract in the development of the network as we work to provide 25% more capacity as part of TfL's continued investment in London Overground.
"It will ensure we remain able to meet the growing demand for London Overground services which, at 89%, have one of the highest levels of passenger satisfaction in London and the South East."