Sunday’s announcement came after a weekend of emergency talks in Switzerland between the two banks and the country’s financial regulators.
The Swiss National Bank said the deal was the best way to restore the confidence of financial markets and to manage risks to the economy.
Credit Suisse said it was not expecting “any disruption to client services”.
“We are fully focused on ensuring a smooth transition and seamless experience for our valued clients and customers,” a spokesperson for the bank told the BBC.
Credit Suisse shareholders were deprived of a vote on the deal and will receive one share in UBS for every 22.48 shares they own, valuing the bank at $3.15bn (£2.6bn).
At the close of business on Friday Credit Suisse was valued at around $8bn.
But the deal has achieved what regulators set out to do – secure a result before the financial markets opened on Monday.
Read more: UBS agrees ’emergency rescue’ of Credit Suisse
