He joins the Dens Park side on a two-year deal, following a season of mixed emotions with the Well.
On his day Johnson is a lethal finisher and the Dee now have a potential Championship top scorer on their books.
Johnson will be key to Dundee success with regular minutes
Last season was a frustrating one for the Englishman. He featured 28 times, mainly in the first half of the campaign, and scored eight times.
From January onwards, Johnson featured just three times, much to the bemusement of most Well fans.
Johnson was easily the best natural finisher at Fir Park. Why Motherwell have decided to let him go after just over 12 months is baffling.
The forward knows where to be at the right time. He’s not a big physical number nine, but he can put himself about. His biggest strength though is his accurate finishing and being where he needs to be at the right time.
Well boss Stephen Robinson likes to play with a big number nine who can press and hassle the backline with physical presence. Johnson just doesn’t suit that role, and despite being the best finisher, he never got a chance because of it.
If Robinson gave him a run of games, Johnson would have thrived at Premiership level. He was a big game player too, netting in matches against Celtic, Rangers and Aberdeen.
The fact that James McPake has convinced him to drop to the Championship can only be seen as a major coup.
Should Dundee provide him with service and regular minutes, Johnson will score plenty for the Dee this term. He gives 110% every game and knows how to finish when the time comes too.
They may just have a Championship top scorer on their hands if things go to plan.