After representing the Ospreys at age grade level, Williams moved on to play for Bridgend Ravens as a teenager, catching the eye despite their relegation from the top flight.
Handed a regional development contract at the age of 19 on the back of his performances that season, Williams then moved to Aberavon and has been a regular fixture at the Port Talbot Athletic Ground, leading the Wizards throughout last season.
He has made four LV= Cup appearances for the Ospreys since his debut in a win over the Dragons at the Brewery Field in January 2012.
After earning himself his professional contract, Williams said he was pleased to have been rewarded for his hard work.
"I've been here for four years now as a development player so it feels good to get this recognition," he said.
"It's been a long road, I've been a part of the set-up for what seems like a long time and seen other players stepping up so I'm pleased to eventually earn the contract I've been working for.
"I've kept my head down and worked hard in training with Aberavon and I'm really pleased that I've been rewarded. You've always got targets, ones you set for yourself and ones that the coaches give you.
"I'm still relatively young so if I can keep improving over the duration of this contract, hopefully I'll get to play more rugby here at the Ospreys."
"Sam is someone who has been in and around our environment for a few years now," commented Rugby Operations Manager, Andy Lloyd.
"He is a good character who has been impressive for Aberavon in the Premiership over a number of years, captaining them last season.
"He has really matured over the last 18 months and it is all credit to him that he has earned a professional contract. He did a decent job for us in the LV= Cup last season, starting three out of our four games and giving us an idea of what he is capable of at this level.
"He's a good rugby player with a good understanding of the game and he's pretty athletic, which is a good combination for a second row. We see him playing a decent amount of rugby for us this year and providing real competition to some of the more established players we have in that position.
"This is another example of a local youngster who we have tracked in club rugby and rewarded for their efforts in the Premiership."