PARIS—French presidential front-runner François Hollande said taxpayers earning over €1 million ($1.35 million) a year would be subjected to a special 75% tax bracket should he be elected, underscoring heightened interest across Europe in raising taxes on the wealthiest individuals.

Speaking on French television late Monday, the Socialist candidate lamented the "considerable increase" in French corporate executives' pay, which he put at €2 million a year on average. "How can we accept that?" asked Mr. Hollande.

His...