Northern has now fully taken over management of the site from former partners East Midlands Railway, and 550 engineers, technicians and other staff such as cleaners have now become Northern employees.
They have promised to make Neville Hill 'a centre of rail engineering excellence' and develop it into a state-of-the-art facility.
The depot on the Leeds to Selby line is two miles from Leeds Station and is often used to stable rolling stock overnight as well as for light and heavy maintenance. There has been a facility on the site since 1899.
East Midlands Railway used to maintain their High Speed Train fleet at the site but left when these were withdrawn from service in May, ceding full control to Northern.
Northern engineering director Jack Commandeur said: “We are delighted to welcome our former East Midlands colleagues into the Northern fold and will continue to provide maintenance support for Northern, LNER and Cross Country trains.
“This is a positive step for rail in the north that will help to deliver more consistent and reliable services for customers, strengthen critical engineering processes and open up future opportunities to develop the depot into a state-of-the-art facility.
“We have ambitious long-term plans for the site and are exploring long term opportunities that we hope will, in time, see the depot transform into an engineering centre of excellence with educational partnerships and development programmes.”