HONG KONG — U.K.-based chip designer ARM Holdings PLC confirmed Monday that it has agreed to a buyout offer worth more than $32 billion from SoftBank Group Corp., marking a significant push for the Japanese telecommunications giant into the mobile internet.

The all-cash deal comes on the heels of SoftBank 9984, -1.08% Chief Executive Masayoshi Son’s decision to take back the reins of the company’s investment strategy from his former deputy and designated successor, Nikesh Arora, who resigned in June.