The former Liverpool defender, 27, is reportedly ready to tie up an £8m move to the Midlands and Rovers boss Sam Allardyce is now resigned to losing the player.
Villa have struggled in the left-back department since Wilfred Bouma sustained a long-term injury last summer, with replacement Nicky Shorey failing to really impress.
Warnock's move could be good for all parties as Villa desperately need new additions to their squad, Blackburn will get a good fee and Warnock will increase his chances of breaking into the Englnd squad ahead of the World Cup next year.
After completing the deal for yet another talented Englishman, O'Neill will turn his attention to strengthening the backbone of his side, which still looks decidedly weak.