The club on Wednesday parted company with Gary Owers with the Gulls sitting in 14th place in the National League South.
They decided not to hang around and Johnson, who left Cheltenham Town last week, is their new boss.
The former Yeovil and Bristol City manager was a National League champion back in 2016 when he guided the Robins back to League Two at the first attempt.
Now he is looking to similar after relegation at Plainmoor and the 62-year-old knows he is in for a hard eight months ahead.
He said: “It has been a crazy 36 hours in meeting Clarke Osborne and his team, understanding the Club, understanding his ambition and resource and seeing the determination to succeed.
“I have been really impressed with the plans to equip Torquay United with the facilities and finance to challenge in the football league and I believe that I can lead the Club back to Division 2 and beyond. It is for these reasons that I have chosen to take up this challenge.
“It’s not going to be easy but a strong professional organisation and determined, resourceful owners provide the tools to succeed.
“I am really looking forward, to meeting everyone and to this challenge. Much work to be done!”