McDonagh to ride for Aga Khan
(Healy Racing Photos)
McDonogh takes over from Johnny Murtagh, whose contract was terminated in August.
The 2006 Irish champion jockey said: "I'm delighted to have been given this amazing chance.
"It's a huge honour and a huge privilege to be riding for His Highness."
McDonogh (32) had already been given a chance to shine aboard the Aga Khan's horses following Murtagh's departure.
He partnered the exciting juvenile Zand, trained by John Oxx, to victory at Leopardstown in October.
McDonogh added: "I've been speaking to Pat Downes, who is His Highness' Irish stud farm manager, for a few days now and I can't wait to get started.
"I already have a bit of an idea about some of the great horses I will hopefully be riding.
"Mr Oxx has already given me some good chances, like when Zand won at Leopardstown.
"It's a great opportunity for me."
The Tony Martin trained Benefficient faces five rivals in what promises to be an intriguing Grade 2 GPG Novices' Chase at Newbury on Thursday.