The Norwegian midfielder scored two goals in 28 matches for Hertha last term and arrives at the Olympic Stadium for an undisclosed fee.
"Hertha BSC is my club, I'm incredibly happy that I'm back here," he beamed.
"I am particularly pleased for the fans. I have always heard and read how much they wanted to see me back at Hertha.
"Now the time has come and that's great."
And sporting director Michael Preetz declared his delight at having landed a long-time target.
"To bring Per Skjelbred finally to Hertha BSC was a big concern for us," he said. "Per is as a footballer and as a human being simply a good boy."
Skjelbred joined Hamburg from Rosenborg in 2011, but was deemed surplus to requirements at the Imtech Arena.