MAIREAD Devlin was once a straight girl who put feelings of "discomfort" in her own body just down to being normal.

But spring 2014 brought a "penny drop" moment.

"I realised I was trans."

In the nearly two years since, Mairead has made the transition from being a female to male, all the while working as a general duties officer in the Queensland police.

The constable, who went to school at Maleny and is stationed at Caboolture, has been open about his transition and said he was yet to experience an adverse reaction.

"I'm at a big station with close to 80 officers and I'm yet to have someone enter a negative opinion," Const Devlin said.

He said in hindsight, there were clues that he missed that his gender and body were not a perfect match.

THEN: Mairead Devlin at the end of year 12 at Maleny State High School in 2011. Warren Lynam

"Heading up to that point, I think there'd been obvious indicators that I just wasn't aware of," he said.

"I just thought a put a lot of the discomfort I had with my own body down to normal body issues.

"Had I known that trans was more than Priscilla, Queen of the Desert, I probably would have come around a lot sooner," he said.

Const Devlin had never had any exposure to anyone who was transgender and always associated "trans" with transvestites who dressed up in women's clothing, as per Priscilla.

But he began to question his sexual identity after the end of a relationship where he had experienced jealousy and envy over another man's body. The feelings were repeated when an acquaintance transitioned from female to male.

"I went through a fairly intense couple of months where I tried to figure everything out. Once I realised, I thought I'm meant to do that."

While some people spend years considering their sexuality, Const Devlin said the shorter time frame had worked better for him.

"I think my mental health wouldn't be as fantastic as it is now if I had waited," he said.

He said it had been difficult to tell others but he had been fortunate to have supportive friends and family.

"My dad is a counsellor and social workers and he said it was normal for people my age to be questioning sexual identity," he said.

"Mum, it definitely came out of the blue for her. She needed a few cups of tea to get over the shock but friends and everyone have been very supportive."

Const Devlin was only months out of training at the police academy at the time and was worried about how co-workers would react but needlessly so, as it has turned out.

"If anyone has any objections to what I'm doing, they're yet to make themselves known to me," he said.

Const Devlin has been through some gender adjustment surgery but keeps the extent private. The 22-year-old has retained the name Mairead which he described as fortunately ambiguous.

The constable raised the LGBTI pride flag outside Queensland Police headquarters in Brisbane for the first time for International Day Against Homophobia and Transphobia celebrations this week.

He said he was "very honoured and humbled" to be asked given there were longer serving officers but he was encouraged as a young officer to take the role as a sign of the future of the organisation.

He said it was important for the community to be aware of the diversity within the Queensland Police Service and realise that officers were working hard for the general public and members of the LGBTI community.