They will race in the RST Superbike and PokerStars Senior TT on the SG5 V4 Norton. Another Australian, veteran British Superbike racer Glenn Richards, has joined the factory team as test rider.

“It was the sheer power of the Norton at this year’s TT that got me interested,” Johnson said. “I was level with Cam down Cronk y Voddy Straight (a 280km/h section) and thought I’d slipstream him but he just pulled away.”

Johnson was on a 220hp BMW Superbike and soon found out how powerful the latest version of the Norton V4 was when he tested it a few months later.

“It makes unbelievable power but the area it needs work on is the delivery of that power,” he said. “I know the factory is doing serious work on this and having watched how Cam has developed the SG Norton over the past two years has given me the confidence to commit to the factory team.”

Johnson, who hails from Adelaide as does Richards, made his TT debut in 2010, winning the Newcomers’ Trophy. This year he became the fastest Aussie ever around the demanding TT course, with a best lap of 131.595 mph. His highest placed result is fourth in the 2014 RL360 Superstock Race and he finished in the top 10 in both the Superbike and Senior TT last year as well as the Superstock and Supersport 2 races.

Donald, a two-time TT winner on Suzukis, confirmed the effort being put into the latest version of Norton’s racer: “We’ve now done a huge amount of development work in the Isle of Man and having that continuity will really help us to make more progress at next year’s TT,” Donald said. “It will be good to have two bikes out and I’m sure Dave and I will be comparing notes every session to help each other.”

Johnson is no stranger to Nortons: “After my whole life seeing Dad ride and work on vintage Nortons, I’m now a Norton factory rider! I’ll be giving it my all.

“Cam Donald as my team-mate is a massive honour and I have known Glenn Richards since 1998 and have seen the great development work he has done for other teams over the years.”

Announcing the expanded team, Norton Motorcycles CEO Stuart Garner said: “This was always going to be a long-term project and we’re definitely on the next stage of our evolution. Running a two-man team with Glenn Richards testing and Mick Grant (famous UK racer and team manager) advising will give us the best opportunity to move things forward even more at next year’s TT.”