De Jong, who started as president and chief executive officer of Mizuho International yesterday, replaces Paul Hearn, a former BNP Paribas debt specialist brought in two and a half years ago to bolster the European business.
Hearn, who stepped down in May but is due to stay on as an adviser until the end of October, is leaving to pursue other interests, a spokeswoman said.
Mizuho has about 400 staff in its London investment banking and securities business. The broader Mizuho group said at the end of 2011 it was cutting 3,000 jobs, or five per cent of its workforce, by 2016 as it merges its retail and banking units.
Hearn chopped and changed some of the London teams, hiring in areas such as high-yield bonds. The bank also now handles bond issues in currencies such as euros and renminbi when it used to focus on yen.
De Jong, who started at ABN Amro in Amsterdam but became country manager in the likes of Germany and Hong Kong, said in a statement that he was pleased to be joining at a time when “Japanese banks can take advantage of the economic conditions in Europe and the United States to ... grow internationally”.