Here are some US successful politicians (holding national or State governor positions) who committed suicide while in office:

Meriwether Lewis (of Lewis and Clark expedition fame) was governor of Louisiana territory when he died of gunshot wounds in 1809. (This is generally thought to have been suicide, but there are some theories that it was murder.)

Thomas Reynolds, governor of Missouri, shot himself while in office in 1844.

Thomas Jefferson Rusk, US senator from Texas committed suicide while in office in 1857.

John Milton, governor of Florida, shot himself while in office at the end of the Civil War, believing, “death would be preferable to reunion”.

James Henry Lane, US Senator from Kansas (and general in the Union Army) shot himself while in office in 1866 after being charged with financial irregularities.

Robert Adams Jr., US Representative from Pennsylvania, shot himself while in office in 1906, despondent over stock speculation losses and the prospect of electoral defeat.

John Arthur Elston, US Representative from California, committed suicide while in office in 1921.

Frank Bosworth Brandegee, US Senator from Connecticut, committed suicide while in office in 1924.

Joseph Medill McCormick, US Senator from Illinois, committed suicide while in office in 1925.

Samuel Austin Kendall, US Representative from Pennsylvania, shot himself while in office in 1933.

Godfrey Gummer Goodwin, US Representative from Minnesota, jumped (or fell) from 5th floor window while in office in 1933.

Marion Anthony Zioncheck, US Representative from Washington, jumped from a window while in office in 1936.

Lester Callaway Hunt, US Senator from Wyoming, shot himself while in office in 1954.

Douglas Hemphill Elliott, US Representative from Pennsylvania, committed suicide through carbon monoxide poisoning while in office in 1960.

William Oswald Mills, US Representative from Maryland, committed suicide while in office in 1973.

John Porter East, US Senator from North Carolina, committed suicide while in office in 1986.

http://politicalgraveyard.com/death/suicide.html

Outside of the US, “world leaders” who committed suicide while in office include; Adolph Hitler, Demosthenes, Cleopatra, Marc Antony, Brutus, Jan Masaryk (Foreign Minister of Czechoslovakia) said to have jumped from a window, though perhaps more likely that he was murdered, Salvador Allende, President of Chile, (though possibly assassinated), and, no doubt others.