"I was on a Development contract down in Munster when Brads (Michael Bradley) phoned me and offered me a spot," explained the 28-year-old.
"I jumped at the chance to play regular Magners League rugby and haven't looked back since. It's taken a while to get to this milestone, I've had a few injuries along the way.
"Amongst other injuries I damaged my crutiate ligament against Munster in 2007 and was out for nine months so that didn't help, but I'm delighted to reach 100 caps for Connacht. It's a huge personal achievement."
Matthews made his debut in Connacht's 13-9 victory over the Cardiff Blues in September 2005 alongside current captain John Muldoon, current assistant coach Dan McFarland and recently-appointed video analyst Conor McPhillips.
He has scored 14 tries for the province and set up dozens more with his hard running and ferocious tackling.
"I've been involved in some great games over the years, beating Munster here at the Sportsground two years ago, beating Bourgoin in the quarter-final of the Amlin Challenge Cup here last season and captaining the side against Munster on St. Stephen's Day this season.
"Hopefully there'll be many more to come. I'm enjoying my rugby more than ever and playing some of the best rugby of my career so I've no intention of giving up just yet!"
Matthews was part of the Ireland 'A' team that won the Churchill Cup in 2009, beating England Saxons in the final. That side also included Connacht's John Muldoon and Sean Cronin.
Connacht's starting line-up for the Edinburgh match shows three changes to the one from last weekend's disappointing defeat to Aironi Rugby.
Matthews starts in place of the injured Niva Ta'auso, while Ronan Loughney and Bernie Upton come in for Brett Wilkinson and Michael Swift in the front row and second row respectively. Swift has a fractured hand.
Hooker Adrian Flavin could also earn his 100th cap this weekend. He is part of a replacements bench which includes fit-again duo Muldoon and Eoin Griffin and Ireland Under-20 scrum half Mark Dolan.
CONNACHT (v Edinburgh): Gavin Duffy; Brian Tuohy, Troy Nathan, Keith Matthews, Fionn Carr; Ian Keatley, Frank Murphy; Ronan Loughney, Sean Cronin, Jamie Hagan, Mike McCarthy, Bernie Upton, Andrew Browne, Johnny O'Connor (capt), Ray Ofisa.
Replacements: Adrian Flavin, Brett Wilkinson, Rodney Ah You, Mike McComish, John Muldoon, Mark Dolan, Eoin Griffin, Shane Monahan.