The London site - its third in the capital - will open on New Oxford Street, while the Cardiff Shack - the company's first in the UK outside London - will open at St David's Shopping Centre.
Both sites are scheduled to open late 2015/early 2016.
Nigel Sherwood, business director of Shake Shack UK said the company was continuing to look for more sites in 'major cities' in the UK.
“This is an extremely exciting time for us at Shake Shack, particularly as we deepen our connection to the UK,” he said. “This winter we’re bringing two incredible new Shacks to two very different, but very fitting spots in the UK. We plan to ensure that not only is each Shack engrained in its community but also becomes a true gathering spot.
"As we grow, we will continue to look for outstanding opportunities in major cities.”
Born in New York City where it was founded by Danny Meyer's Union Square Hospitality Group, Shake Shack's offering centres around 100 per cent all-natural Angus beef burgers, griddled-crisp flat-top dogs, fresh-made frozen custard and crinkle cut fries.
Its first site opened in Covent Garden in 2013 before a second opened at Westfield Stratford last month.