"I will today announce that I will no longer stand for re-election next year," he told a conference call after Sampo's annual shareholder meeting.

Wahlroos, who turns 70 later this year, said he would also step down as chairman of Finnish forestry group UPM Kymmene next year.

Sampo told the market that the Norway-based holding company Becasse, which is owned by Wahlroos, had sold 900,000 Sampo shares.

"I've been transferring assets to my children and I have preferred to transfer the most long-term assets in the portfolio, which typically would be the Sampo shares," he said, adding that his holding company would stay overweight in Sampo even after his retirement.

Wahlroos, who was previously chairman of the Nordic region's largest lender Nordea's, said other reasons for the large transactions included restructuring his family business on private equity and private debt investments.

Following the transactions, Wahlroos said his family held about 3.7 million Sampo shares, or a roughly 0.7% stake.

(Reporting by Anne Kauranen; Editing by Louise Heavens and Edmund Blair)