Goldman Sachs' new online retail bank Marcus has "exceeded every expectation" in its debut on the international stage, according to its managing director.

Des McDaid at Goldman Sachs told CNBC that the digital bank has won over 100,000 U.K. customers since its launch at the end of September. Marcus' online platform promises customers a 1.5 percent interest rates on their savings, the highest rate in the market for instant access accounts, according to data firm Moneyfacts.

"U.K. savers have been waiting for something for a long time," McDaid said Tuesday from the LendIt fintech conference in London. "We said we'd put the interest back into savings. We did that by creating a bit of a buzz, a bit of a noise around our launch, and it's just taken off."

McDaid said Goldman is committed to its business in the U.K. despite questions facing the country's financial services industry after Brexit. He added uncertainty in the economic outlook from Brexit is one reason consumers need to save money.

"We're in the U.K. to stay and hopefully U.K. savers know that," McDaid said.