The planet is our closest, yet perhaps most overlooked, neighbour and the missions come after decades of exploring other worlds.
The space agency's new administrator, Bill Nelson, announced the missions during his first major address to employees on Wednesday.
“These two sister missions both aim to understand how Venus became an inferno-like world capable of melting lead at the surface,” he said.
One mission named DaVinci Plus will analyze the thick, cloudy Venusian atmosphere in an attempt to determine whether the inferno planet ever had an ocean and was possibly habitable.
A small craft will plunge through the atmosphere to measure the gases. It will be the first US-led mission to the Venusian atmosphere since 1978.
The other mission, called Veritas, will seek a geologic history by mapping the rocky planet's surface.
“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, Nasa scientist Tom Wagner said.
“It will be as if we have rediscovered the planet.”
Nasa's top science official, Thomas Zurbuchen, calls it “a new decade of Venus”.
Each mission — launching sometime around 2028 to 2030 — will receive $500 million for development under Nasa's Discovery program.
The missions saw off two other proposed projects, to Jupiter's moon Io and Neptune's icy moon Triton.
The US and the former Soviet Union sent multiple spacecraft to Venus in the early days of space exploration.
Nasa's Mariner 2 performed the first successful flyby in 1962, and the Soviets' Venera 7 made the first successful landing in 1970.
In 1989, Nasa used a space shuttle to send its Magellan spacecraft into orbit around Venus. The European Space Agency put a spacecraft around Venus in 2006.
Additional reporting by the Associated Press.