The 20-year-old left-back has returned to Brunton Park after a successful two-month stint earlier this season which ended at the back end of November.
"We know all about Conor and we're delighted that we've been able to get him back," manager Graham Kavanagh told the club's official website.
"He really enjoyed his spell with us before Christmas and we think we all saw how much he improved and added to the squad as the weeks went by.
"Hull obviously think very highly of him and it's great that they feel this is a good place for him to be.
"He's a great lad with a fantastic attitude and we're looking forward to working with him again through a very busy second half of the season."
Townsend's returns follow hot on the heels of Tom Lawrence's loan extension from Manchester United earlier on Thursday.
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- Graham Kavanagh