Each mission will receive £350 million ($500 million) for development under Nasa’s Discovery programme.
After decades of exploring other worlds, the Space agency will return to study Earth's closest neighbour and the solar system's hottest planet.
The two missions were announced by new Nasa administrator Bill Nelson in his first major address to employees.
“These two sister missions both aim to understand how Venus became an inferno-like world capable of melting lead at the surface,” Mr Nelson said.
One mission named DaVinci Plus will determine whether the planet ever had an ocean and whether it was ever habitable. A small spacecraft will analyse the thick, cloudy Venusian atmosphere.
It will be the first US-led mission to the Venusian atmosphere since 1978.
The second mission named Veritas will mapping the rocky planet’s surface and study its geologic history.
Nasa scientist Tom Wagner said: “It is astounding how little we know about Venus,” but the new missions will give fresh views of the planet’s atmosphere, made up mostly of carbon dioxide, down to the core. It will be as if we have rediscovered the planet.”
Nasa's top science official, Thomas Zurbuchen, calls it “a new decade of Venus.”
The missions were chosen over two other proposed projects: to study Jupiter’s moon Io and Neptune’s icy moon Triton.
Scientists studied Venus in the early days of space exploration after the US and the former Soviet Union sent multiple spacecraft to the planet.
Nasa’s Mariner 2 performed the first successful flyby in 1962, and the Soviets’ Venera 7 made the first successful landing in 1970.
Nasa used a space shuttle to send its Magellan spacecraft into orbit around Venus in 1989.
The European Space Agency put a spacecraft around Venus in 2006.