The new four-level car park will provide 278 patient and visitor car parking spaces.
It has been designed to improve the flow of cars, reducing queuing and congestion along Lewsey Road.
Cycling facilities will also be available including 40 cycling spaces for patients and 200 for staff, as well as staff changing and shower amenities.
David Carter, chief executive at Bedfordshire Hospitals NHS Foundation Trust, said: “We are delighted to be opening this multi-storey car park which we know will be very welcomed by our patients and visitors.
"At the moment, due to the current visiting restrictions in place to manage the risk of spreading Covid-19, the public are asked not to attend the hospital site unless they have an appointment, or are visiting under exceptional circumstances but once we return to normal business the expanded capacity will greatly improve the experience of those visiting the L&D.
“The cycling facilities are also a great way to encourage more of our staff to run, ride a bike or walk to work.
“I’d like to thank our patients, visitors and staff for their patience over the past few months while this work has been completed.
“This is an exciting time as we complete one of many redevelopment projects on both our hospital's sites.”