The DCNS decision was taken by Thales at its board of directors' meeting this week.
Thales, which has headquarters in Paris, already has a 25 percent stake in DCNS, acquired in 2007. It plans to increase that to 35 percent under an option contained in the earlier buy.
"This decision follows on the increasingly closer partnership between the two companies since 2007 as well as the successful cooperation between Thales and DCNS in France and on export markets," Thales said.
"It is a significant step toward strategic alliances in the naval domain in Europe and, in accordance with the agreements signed in 2007, will give rise to additional rights for Thales in the governance of DCNS, thereby strengthening the cooperation between the two companies."
Thales also reported it has entered talks with the Nexter Group on collaboration between their respective ammunition production companies in conjunction with Thales obtaining a minority stake in the company.
The project would bring together Nexter Munitions and TDA Armaments.
"This project is a further step in the consolidation of the defense industry in Europe, benefiting both competitiveness and employment," Thales said.