The 28-year old Australian midfielder has had his deal with Bristol City cancelled in order to join the Lilywhites on a permanent basis after arriving initially on loan in November.
Kilkenny was set to come out of contract at Deepdale this week but the Robins allowed him out of his contract so he could continue his career under his former Leeds United boss Simon Grayson in Lancashire.
"I have enjoyed my time here so far, everyone has been so welcoming," Kilkenny said.
"I already knew the manager and his assistant from my time at Leeds and hopefully the results and performances we have had so far can carry on.
"This is a brand new start for me and it is a great club so I am looking forward to it. We want to kick on, keep winning and hopefully we'll be right up there at the end of the season."
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