La Montre Hermès said in a statement it had raised its previous 32.5 percent stake it has held since September 2011 in the Swiss family-run firm to an unspecified level giving it a controlling majority share.
"For Hermes, this operation is a natural part of a continuing effort to master the craft of watchmaking," the French group said.
Joseph Erard Holding specialises in making watch casings. Hermes last year took control of another Swiss company, Nateber, which makes watch faces. In 2006, Hermes took a stake in Vaucher, a Swiss company that makes mechanical movements inside watches.
Watches are a small but growing segment in Hermès's product lines. Last year, the subsidiary expanded sales 17 percent to €173 million ($225 million), which accounts for five percent of Hermes total group revenues.