The terms of the deal will see Credit Suisse shareholders receive 1 UBS share for every 22.48 Credit Suisse shares they hold.
"This acquisition is attractive for UBS shareholders but, let us be clear, as far as Credit Suisse is concerned, this is an emergency rescue.
The Swiss National Bank pledged a loan of up to 100 billion Swiss francs ($108 billion) to support the takeover.
UBS initially offered to buy Credit Suisse for around $1 billion Sunday, according to multiple media reports.
It reported a full-year net loss of 7.3 billion Swiss francs for 2022 and expects a further "substantial" loss in 2023.