The former Mountain Creek State High School student was killed when he was struck by a tree branch during the exercise at Shoalwater Bay, near Rockhampton, on Thursday morning.

In a statement, Mr Reddan's family paid tribute to the young soldier, who joined the Army cadets when he was 14, saying they were "unbelievably saddened" by the death of their loved one.

"We will always remember Stuart as a charming, happy, fun-loving young man.

"He died doing what he loved. Stuart was very, very passionate about being a soldier and he loved every moment in the Army and his mates.

"We would like to thank everyone for their loving words, their happy memories of Stuart and their support.

"We would also like to thank the soldiers who provided first aid to Stuart and were with him at the time. We send our heart felt thanks out to these soldiers. We know you did your best to save him."

The victim's brother Tom Reddan also took to Facebook on Thursday night to pay tribute to his "baby brother".

"I miss you like crazy bro and wish you were still here with me. Rest In Peace My Brother," he wrote.

Friends also paid tribute on Facebook.

"I am thinking of all the great times we had as kids and it looks like Stuart grew into a great man," wrote Ashley Mclaughlin.

"Words cannot even comprehend the pain of losing a good friend.," Hannah Smith wrote.

"I just can't believe it. Stuart Reddan, you were one in a million. Kind to everyone, put others before even thinking about yourself.

"I'll forever cherish you walking me home so often and all the laughs we'd have along the way.

"I thank you for showing compassion and an open mind to absolutely everything."

His sister Erin Reddan shared a family photo of her, Tom, Stuart and their mother Laura Dyne to her page.

Mountain Creek State High School senior school principal Andrew Stone said Mr Reddan had been elected school captain in 2013 and 2014 and would be remembered as a hardworking, generous and enthusiastic young man.

"Stuart was generous, kind and softly spoken," Mr Stone said.

"He will be sorely missed and forever remain in our thoughts."

Mr Stone said the former student was also a talented bass trombonist and had a passion for music.

"Our sincere sympathies go out to his family, friends and loved ones during this difficult time," he said.

The Army has extended its sympathies to the soldier's family and friends.

Queensland Police are investigating and are expected to prepare a report for the coroner.