The project included the installation of lifts giving customers step-free access from the new ticket hall to the Circle and Hammersmith & City line platforms.
Earlier work added a new entrance from the Paddington Basin side of the station, a spacious new station concourse, better access to the mainline concourse, two new stairways, improved CCTV and extended platforms to accommodate new, longer air-conditioned trains.
More than 60,000 passengers currently use the Hammersmith & City station every day, with demand growing as a result of the extension of the Circle line to Hammersmith.
When Crossrail services begin in 2018, passenger numbers will increase further.
Paddington station will be a key point on the Crossrail route as it runs through central London. Twenty-four trains an hour will pass through the station in each direction during peak periods.