The Wellington-born mother of two first worked on Earnslaw in 1990 after running the Walter Peak Catamaran when she was just 21.
She decided to work as a deckhand on the steamship "thinking it would be a great job to tell my grandchildren about - that I worked on the Earnslaw".
Now, she will be able to tell her grandchildren about an even better job.
Three years ago, Ms McIlroy returned to Earnslaw, again as a deckhand, a job she describes as the skipper's "right hand".
"I guess there was an opportunity [to become a skipper] . . . but I had to be really patient."
After 12 months' training under the watchful eye of Senior Launchmaster Graham Moore-Carter, Ms McIlroy was given final approval by Real Journey's chief launchmaster and safe ship manager Peter Bloxham on January 27 after her handling of the grand old lady was assessed in all weather conditions.
"People have made more of a fuss than I would have considered this to be - everyone seems pretty pleased.
"It's about the changing world and the equal opportunities.
"It's an absolute privilege . . . 50 years ago I would have been told to `get back down to that galley and make the scones and the tea'.
Ms McIlroy said every day was "a real team effort", with one of the most important aspects of her new job being to work closely with the stokers and engineers in the boiler room.
For the self-confessed water lover, who spends her free time at the helm of her own boat, Little Song, a 5m trailer sailer, or in the Catlins diving, surfing and swimming, captaining Earnslaw was a dream come true.
Real Journeys Queenstown general manager Tracey Maclaren said the company was delighted Ms McIlroy had achieved the milestone.
