New Jersey used to have a common practice of dual office holding. The longest modern combined tenure that comes to mind immediately is Leonard T. Connors Jr.—simultaneously the mayor of Surf City, New Jersey (1966–2015) and a State Senator (1982–2008) for a combined seventy-five years.
Dual office holding was the norm in France until it was banned in 2017.
Most national politicians were mayors at the same time. For example, Jacques Chirac was Mayor of Paris during his term as Prime Minister between 1986 and 1988.
