The spacewalk had been expected to last about six hours, but had to be cut short due to a "a small amount of water" in Kopra's helmet, NASA tweeted. They had completed their most vital tasks for the excursion, so out of an abundance of caution the walk was ended early.
The astronauts waiting anxiously inside pulled off Kopra's helmet, then measured the water that had leaked, presumably from the suit's cooling system. Nevertheless, the incident echoed a scary episode in 2013 when Italian astronaut Luca Parmitano almost drowned inside his spacesuit.
During the second half of the EVA, the astronauts will lay cables for new docking ports and reinstall a valve that was removed previous year.
It took Major Peake and Coloner Kopra fifteen minutes to get back to the Quest airlock after being told to return to the space station.
Space station commander Scott Kelly reported that he filled a syringe with about 15 cubic centimeters of water.
While tuning in, you can distinguish between the members of Team Tim by looking for Kopra who has red stripes on his suit, while Peake has none. Today the nation cheered and breathed a sigh of relief when he was safely back in the space station.
Mr Peake said he felt "exhilarated" about his upcoming spacewalk but had "no time to dwell on these emotions".
The leak in Parmitano's helmet was so severe that floating water had covered his eyes, ears, nose and part of his mouth.
NASA said Kopra and Peake were never in danger and the astronauts will take a water sample to eventually determine what caused the water to form inside Kopra's helmet.
The leak increased as Kopra and Peake returned to the airlock.
The pair will work in 45-minute blocks of daylight, then complete darkness, as the ISS orbits Earth every 90 minutes.
The European Space Agency astronaut follows in Michael Foale's footsteps - who became the first Brit to carry out a spacewalk in 1995, albeit with a USA banner.
Peake was able to see the water droplet within Kopra's suit describing it as "less than a golfball" in size.
Tim Peake readies his tools for the crucial fix of the space station's voltage regulator.