Keane is poised to stage a media conference at lunch-time after the confirmation of his temporary switch from Galaxy until Major League Soccer restarts in March.
Villa were waiting to receive the final piece of paperwork during the early hours after Keane joined up with them for training at the start of this week.
He will be in contention to make his debut against Everton - and his LA Galaxy team-mate Landon Donovan - in Saturday's Barclays Premier League clash at Villa Park.
Villa manager Alex McLeish hopes Keane can provide the same sort of spark as another on MLS loan player Thierry Henry has achieved after rejoining Arsenal.
New York Red Bulls striker Henry marked the start of his second spell at Arsenal by scoring the winner in the FA Cup triumph over Leeds.
McLeish said: "I saw Thierry Henry's goal the other night and it was a fantastic moment regardless of which team you support. I thought 'wow, it would be good if Robbie can make that kind of impact'."
Keane moved to Galaxy from Tottenham last summer after spending the second half of last season on loan at West Ham.
But he is keen to maintain his sharpness during the current close season in America ahead of skippering his country in this summer's Euro 2012 finals in Poland and Ukraine.
Villa fit the bill for the 31-year-old and McLeish hopes Keane's experience can aid his young squad, especially with Emile Heskey sidelined for a month with his Achilles injury.