He said there were times during the run when his entire body was aching and he struggled to go on, but knowing he was helping raise money for a worthy cause kept him going.
"The finish line couldn't come quick enough. It was just a huge relief to get there," he said. "Knowing that what I was doing was going to help people, there was no way I was going to give up."
It was Mr Weaver's third Rotorua Marathon, after he completed one 20 years ago, then another 10 years ago.
"It certainly doesn't get any easier," he said.
The toughest part was running the long, straight roads near the airport, he said.
Meanwhile fellow staff member Gerald Pinckneysaid it was his first, and perhaps his last, half marathon.
"This cause is probably the only reason I'd ever get my arse off the couch and run. I don't think I'll be doing it in a hurry anytime soon," he said.
Reporoa VETPlus marketing manager Treena Braithwaite said the team had raised about $3000 for the charities so far, but hoped to raise a total of $5000.
The funds will be split between the two charities.