Bosses at Preston Council and Lancashire County Council, who have been working together on the Harris re-imagined project, have agreed to “streamline” the opening times.
The whole building will now be open on Sundays, with later opening on a Wednesday when the museum, gallery and library will be open until 8pm, and the cafe and shop will be open until 7.30pm.
Coun Peter Kelly, Preston Council’s cabinet member for culture and leisure, said: “It’s a small step but a really important one.
“It shows we mean business and are absolutely determined to change the Harris into Lancashire’s, and one of the region’s, premier attractions.
“Through this change, people will now be able to enjoy the Harris in its entirety on a Sunday – which is obviously great news for visitors, families and library users alike.”
County Coun Marcus Johnstone said: “This is a really positive move forward.
“It’s important that we are open when the public want to visit us.
“We’ve worked closely with Preston Council and also taken important feedback from the public consultation on board to achieve this.
“The Harris can now continue to go from strength to strength.”
The new opening times will come into force on Saturday.