It might seem like an odd hobby, but for the past 25 years the former mechanical engineer has been lending his skills to help out St Vincent de Paul.

The unconventional method of volunteering has been of great benefit to the charity store, which has Mr Smyth restoring watches donated from Queanbeyan and the ACT.

Well-worn timepieces which are often thrown in with a bag of clothes and delivered to the op shop are usually in need of a service, and a new battery. Without them, they're basically worthless.

Mr Smyth said he not only changes the batteries, he also replaces the bands and does repairs, all at no cost to the charity service.

"I did a few courses to learn to fix watches," Mr Smyth said.

"I put batteries in them and I clean them up, re-oil them and reset them."

"We get a few Longines, they're quite an expensive watch, we get a few of the really expensive ones.

"We've had a few Rolexes," he said.

Described as an "amazing volunteer", Mr Smyth said he likes doing his little bit for charity. He described how he came to be the watch guru, saying one thing just led to another.

"One Sunday at church my wife and I were looking for some people to make lunches or dinner for, poor people. We started making dinners for them and then I started volunteering at St Vincent de Paul."

Mr Smyth came to Queanbeyan in 1990, and before that lived in Canberra. Originally from Ireland, he celebrated his 90th birthday at the Canberra Yacht Club with family on February 15.

Mr Smyth said despite his age, he planned to keep volunteering for the charity.

"As long as I can keep going, I will," he said.