The cluster, called IDCS J1426.5+3508 (IDCS 1426), is located 10 billion light years from Earth.
NASA used data from a number of observatories to make the most detailed study yet of the galaxy cluster.
IDCS 1426 has been found to weigh as much as 500 trillion suns
No other galaxy clusters match IDCS in terms of its youth and mass
Astronomers are seeing the galaxy cluster as it was when the universe was 3.8 billion years old
Other massive galaxy clusters from the early years of the universe have been found, but none of them match the mass and youth of IDCS 1426.
Professor Mark Brodwin from the University of Missouri lead the study, which NASA hopes will them help understand how mega structures like IDCS 1426 formed and evolved early in the Universe.
"We are really pushing the boundaries with this discovery," Professor Brodwin said.
"As one of the earliest massive structures to form in the Universe, this cluster sets a high bar for theories that attempt to explain how clusters and galaxies evolve."
The young galaxy is so far away the light detected from it is from when the Universe was roughly a quarter of its current age.
That means astronomers are observing it from when the Universe was only 3.8 billion years old.
Galaxy clusters, literally a group of hundreds to thousands of galaxies, are the largest objects in the Universe bound together by gravity and scientists believe they should take several billion years to form.
ICDS 1426 was first discovered by the Spitzer Space Telescope in 2012 and has been observed by the Hubble Space Telescope and the Keck Observatory.
Data from the study reveals an over dense core dislodged from the cluster centre, which scientists say could be due to merging with another developing cluster 500 million years prior to what they are seeing now.
Study co-author Assistant Professor Michael McDonald from Massachusetts Institute of Technology said mergers with other groups and clusters of galaxies should have been more common early in the history of the Universe.
"That appears to have played an important part in this young cluster's rapid formation."
Another co-author of the study, Doctor Anthony Gonzalez from the University of Florida, said the study does not change their current understandings of clusters.
"The presence of this massive galaxy cluster in the early Universe doesn't upset our current understanding of cosmology," Dr Gonzalez said.
"It does, however, give us more information to work with as we refine our models."
The study also found around 90 per cent of the mass of the cluster is dark matter, a mysterious substance detected through its gravitational pull on normal matter composed of atoms.