TOKYO—SoftBank Group Corp.’s quarterly operating profit rose 49%, lifted by rising valuations on investments in startups such as Indian e-commerce company Flipkart Group and U.S. shared-office firm WeWork Cos.

SoftBank’s $92 billion Vision Fund and a $6 billion affiliate together earned a quarterly profit of ¥240 billion ($2.16 billion), double what the fund made in the same quarter last year, the company said. That and a one-time gain from the sale of a majority stake in the Chinese operations of U.K. chip designer Arm Holdings...