Her intervention is a major boost to The Daily Express's Save Our Libraries Crusade, which is calling on councils to rethink.
Ms Dorries, 64, said £5million would be made available in February to enable library services to upgrade buildings and technology so they are better placed to respond to the changing ways people use them.
She said: "I want to thank libraries up and down the country for all they do - something the Daily Express has done a great job of highlighting through its campaign. They are a lifeline to millions of people - particularly during Covid.
"They are there for those who don't have a computer at home, or can't afford wifi, or to buy books for their kids. Or for those who are lonely and need friendly support, libraries connect them with their communities.
"If I have one mission as Culture Secretary, it's to open doors for those who need it the most. Libraries are the front line for that effort and I'll press councils hard to invest in libraries because of the enormous value they provide." Research shows at least 800 libraries have been closed in a decade, despite the soaring salaries of fat cat council bosses.
In many cases councils say they have kept libraries open but, in fact, they have dumped them on to volunteers to run. There are now thought to be 500 volunteer libraries in England.
The accelerated rate of library closures comes as millions of households see their council tax bills rise at the same time town hall chiefs enjoy big pay rises.
Some 2,500 council employees are earning £100,000 or more.