Displays can once again be viewed from tomorrow (Friday) following the building's closure in January last year for essential repairs.
But while work was underway, a barrel-shaped glazed roof in the first-floor Central Court Gallery was discovered.
This structure had remained hidden above a ceiling for more than 40 years.
Sarah Brown, principal keeper at the gallery, said: "We are delighted that Leeds Art Gallery is open once again and transformed.
"The refurbishment of the original Victorian glass roof has enabled us to create light-filled first floor galleries and present the world-class collection as it has never been seen before.
"We have revealed the original stunning Central Court for the first time in over fifty years to create a beautiful new gallery for visitors to enjoy.”
The new space is marked by the presentation of British sculptor Alison Wilding RA’s renowned sculpture, Arena (2000), recently gifted from the Contemporary Art Society.
Also marking the reopening of the gallery, the works of influential German artist Joseph Beuys (1921 - 1986) are exhibited in Leeds for the first time since 1983.
Significant works - such as one of the last sculptures made by Beuys, Scala Napoletana (1985) - feature across the three ground-floor galleries, alongside works on paper and vitrines containing objects related to his performances or ‘Actions’.
The exhibition is drawn from the ARTIST ROOMS collection of international modern and contemporary art jointly owned by the National Galleries of Scotland and Tate, and accompanied by a public programme of talks and events, aimed at engaging young audiences.
The collection was established in 2008 through The d'Offay Donation and is displayed in museums and galleries across the UK through a touring programme supported by Arts Council England, Art Fund and Creative Scotland.
The opening programme also features the presentation of new acquisitions by leading contemporary artists, as part of Leeds Art Gallery’s support of living artists and their work.
Recent acquisitions on show include young LA-based artist Martine Syms, whose two-channel video A Pilot For A Show About Nowhere (2015) has been gifted to Leeds Art Gallery through the Valeria Napoleone XX Contemporary Art Society (VNXXCAS) initiative.
Leeds Art Gallery is the first museum to receive a work through the VNXXCAS scheme that addresses the representation of female artists within public collections.
An additional highlight is the new Art Happens commission, Xanadu, by the German abstract artist Lothar Götz - a wall painting that links the upper and lower galleries, drawing the viewer up the stairs to the new light-filled renovated galleries above.
The new collection displays feature works not seen for a generation – including the first opportunity to experience an extensive display of watercolours by John Sell Cotman, the sculpture Maternity (1910-11) by Sir Jacob Epstein; and works on paper by Mexican artist Diego Rivera.
The gallery’s extensive sculptures are presented in collection displays across galleries on both floors featuring artists including Alexander Calder, Tony Cragg and Simon Fujiwara.
The Ziff Gallery focuses on the first 10 years of the Leeds Art Gallery Collection, with the South Gallery focusing on the last 10 years of acquisitions.
Leader of Leeds City Council, Coun Judith Blake, said: “Leeds Art Gallery is a wonderful and iconic element of our city’s fantastic cultural offer and we cannot wait to see the galleries open their doors to the public once again this October.
"Now that we are moving full steam ahead with our 2023 European Capital of Culture bid, it is brilliant to see the return of Leeds Art Gallery which, internationally recognised and celebrated, will offer another timely reminder of why our bid is so varied and strong.”