The new-look Uxbridge library will reopen next month.
The borough's flagship library in High Street closed in March last year for the renovation, and now has more computers, a new spacious layout over six floors, an expanded local studies and archives service, and a cafe.
It will also have longer opening hours.
The ribbon will be cut at 1pm on Monday, April 7.
It caps off the council's £10million investment programme, with all of the borough's 17 libraries having been improved.
Leader of Hillingdon Council Ray Puddifoot said: "The transformation of Uxbridge Library is nothing short of spectacular and I am sure residents will agree. In the space of a year we have transformed a worn out but well used facility into a state-of-the-art library fit for the 21st century.
"Whilst other councils are closing libraries or reducing opening times, with the re-opening of Uxbridge Library we will have rebuilt or refurbished every one of ours - the only council in the country to do so."
For the past year, people have been using a temporary library in the nearby Pavilions shopping centre.
Uxbridge library will now be open from 8am to 8pm between Monday and Thursday; 8am-5.30pm on Fridays; 9am-5.30pm on Saturdays, and 11am-5pm on Sundays.