The 30-year-old forward has found the net just twice this season in 12 Second Division games. He turned down a move to Kidderminster, an instead goes to Shrewsbury Town in a £15,000 transfer, signing a 2½-year contract.
He said: "I don't want to play Conference football but I've come here because Shrewsbury are pushing for promotion. That's the main aim and hopefully I can give them that little bit of a cutting edge and we can go up."
Darby scored 36 goals in all competitions during a spell of just over 2 years at Boothferry Park. Previously he had been at Torquay and Doncaster before joining City, and then left for Notts County on a free transfer in 1998. He made a brief return to Hull in March 1999 in a loan spell, before going to Rushden & Diamonds 3 years ago.