In finding it the scientists, including Dr Richard McMahon from Cambridge University, have displaced the previous record-holder just six weeks after it was discovered.
But Dr McMahon also hinted that his team could be on the verge of discovering many more such "infant" galaxies from the edge of time. He told the journal Science News that "we have a technique for searching for distant galaxies ... We're in new territory here."
Mark Dickinson, at Johns Hopkins University in Baltimore, said: "It's quite plausible that some of these [galaxies] are young objects that are going off for the first time and making stars."
Such early starbirth could have key lessons for scientists. Esther Hu, of the University of Hawaii in Honolulu, said: "As any mother could tell you, a year's growth makes a much bigger difference in appearance and character in a toddler than in someone aged 20."
The newly-found galaxy lies some 12.3 billion light years from the Earth. From that distance, its light would have started travelling towards us when the universe was less than 800 million years-old - about one-fourteenth of its present age, generally estimated at around 13 billion years.
The astronomers discovered it by the "red shift" of its light - the amount of stretching in the wavelengths, caused by the ongoing expansion of the universe.
With everything in the universe moving away from everything else as the impetus from the Big Bang makes space expand, the size of the red shift is the key element in measuring absolute distance.
The latest sighting was made with one of the two 10-metre twin Keck telescopes on Mount Mauna Kea, Hawaii, the world's most powerful optical observatories.
The new galaxy's age, dating from about 60 million years earlier in cosmic history than the previous record holder, a galaxy found by another team in March, could hold significant information for astronomers. Full details of the discovery are to be published in the journal Astrophysical Journal Letters.
The astronomers found the galaxy by looking for a particular type of high-energy radiation emitted by hydrogen atoms as massive stars form.Reuse content