Dublin-based Assets Models has signed the former Sullivan Upper School girl.
Only last week Holly was photographed looking fabulous at a Miss Ireland heat in a low-cut nude-coloured body-con dress.
Holly confirmed that modelling is "something that I never thought about before I was asked".
The university student continued: "But I was asked to do it and it's an ideal time to try new things."
Carol Farrelly from Assets Models, added: "We think she is going to do really well".
Meanwhile McIlroy's agent, Chubby Chandler, confirmed Holly was in the process of packing up her things following the couple’s shock break-up last month.
He added that no firm date for her departure from the house in Moneyreagh, Co Down, has been discussed.
The pair, who were childhood sweethearts, broke up just before US Open champion Rory’s under-par performance at The Open in Sandwich.
Since then the Holywood man has been linked with Monaco-based Danish tennis ace Caroline Wozniacki.
The pair met shortly after Rory won his first Major and are believed to have spent five days together in the south of France a fortnight ago.
According to his agent, part of the reason for Rory’s desire to spend more time away from the UK is the goldfish bowl existence he has endured since that stunning US Open victory in June.
The world number four announced his intention to spend more time in the United States — he's shopping around for a new place in Florida — just before the WGC Bridgestone Invitational event, which got under way in Ohio yesterday.
He is not expected back in Northern Ireland until the end of August after the final Major of the year, the USPGA championship in Atlanta, Georgia.
Meanwhile, Holly, whose friends and fans have rallied around her in support following the split, has been posting regular updates on Twitter.
And she recently used the public social networking forum to post photos of herself waterskiing in Dubai — where Rory has considerable business interests — and her new pink hairstyle.
Last week the pretty gymnast and cheerleader told followers she was “making cardboard boxes along with bubble wrap and sellotape”, perhaps signalling that she was getting ready to move.
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