Cubestormer 3, designed by David Gilday and Mike Dobson, recorded a time of 3.253 seconds at Birmingham's NEC.
The previous record of 5.27 seconds was set by the same design team three years ago.
Craig Glenday, editor in chief of Guinness World Records, was at the NEC to verify the claim as well as two other records set by Mr Gilday at the Big Bang Science and engineering fair.
The robot uses a mobile phone to take pictures of the Rubik's Cube and then works out the quickest way to solve it, using four robotic hands.
The robot is powered by an ARM processor. Mr Gilday, a principal engineer at ARM, and Mr Dobson took 18 months to design and build the robot in their spare time.
Mr Gilday said the attempt was "a bit of fun".
"Our real focus is to demonstrate what can be achieved with readily available technology to inspire young minds into taking a greater interest in science, technology, engineering and mathematics," he said.
"We knew Cubestormer 3 had the potential to beat the existing record but with the robot performing physical operations quicker than the human eye can see there's always an element of risk.
"Our big challenge now is working out if it's possible to make it go even faster."
Mr Gilday also set new new records during the Big Bang fair for the fastest completion of 4x4x4 and 9x9x9 cubes, which are considerably more complicated than the classic 3x3x3 Rubik's Cube.
A robot has broken the world record for the fastest solving of a Rubik's Cube.