NASA project manager Andy Driesman said: "We will fly by Venus seven times throughout the mission".
Thousands of spectators turned up at the launch site on Sunday, including Eugene Parker, the 91-year-old astrophysicist the spacecraft is named after.
The Parker Solar Probe during final pre-launch processing, its white heat shield visible at the top.
Running 24 hours late because of a last-minute countdown glitch Saturday, the trek began at 3:31 a.m. EDT (GMT-4) Sunday when the 233-foot-tall Delta's three hydrogen-fueled Aerojet-Rocketdyne RS-68A main engines ignited with a rush of brilliant orange flame and quickly throttled up to 2.1 million pounds of thrust. It eventually will get within 3.8 million (6 million kilometers) of the surface in the years ahead, staying comfortably cool despite the extreme heat and radiation, and allowing scientists to vicariously explore the sun in a way never before possible.More news: Clerical error lands wrong Thomas Fleetwood check for $154K
It is travelling on board the Delta-IV Heavy rocket, which will hurl the probe into the inner Solar System.
It was the first rocket launch ever witnessed by Parker, professor emeritus at the University of Chicago.
The probe is created to plunge into the Sun's atmosphere, known as the corona, during a seven-year mission.
"I have learnt a very important lesson of my professional scientific career from him: to be generous to the ideas of others, as long as they are not obviously wrong, and even if they contradict my own personal views", he said.More news: Alisson set for debut against West Ham United
NASA's science mission chief, Thomas Zurbuchen, was thrilled not only with the launch, but Parker's presence.
The car-sized spacecraft will speed through space at 430,000mph - coming within four million miles of the Earth's nearest star by 2024.
The project, with a $1.5 billion price tag, is the first major mission under NASA's Living With a Star program.
Not only is the corona about 300 times hotter than the Sun's surface, but it also hurls powerful plasma and energetic particles that can unleash geomagnetic space storms, wreaking havoc on Earth by disrupting the power grid.
Yanping Guo, who designed the mission trajectory, said: "The launch energy to reach the Sun is 55 times that required to get to Mars, and two times that needed to get to Pluto".More news: Pogba gives cryptic response on United future
Sensors will make certain the heat shield faces the sun at the right times and it will correct itself if it ends up at the wrong angle. His 1958 paper was initially ridiculed but has come to be central to our understanding of the solar system and beyond.