"I don't commit myself to anything unless I can do it 100 per cent. I want to play games and I want to win games for London Welsh," said 34-year-old Parker.
"I know how good a coach Lyn is and what style of rugby he wants to play, and that was one of the major factors behind my decision to join the club. I also get on very well with him.
"It's also fresh start for me in London. I want to play some good rugby and hopefully I'll enjoy my time at the club."
Parker made 31 appearances for Wales, scoring six tries, and was part of the side which won the Grand Slam in 2008. He was also selected for Wales' Rugby World Cup squads in 2003 and 2007.
Having made his international debut at Wrexham against Romania in November 2002, he featured in World Cup competition less than 12 months later. He was a try scorer in Wales' heroic pool stage defeat to New Zealand but picked up an injury in the act of scoring which ruled him out of the quarter-final clash with England.
The following year he was in the side which lost 26-25 to the All Blacks at the Millennium Stadium and a year on he helped Wales to a thrilling two-point win over Australia in Cardiff.
In 2008 he started Wales' 26-19 victory over England at Twickenham on the way to a second Grand Slam in three years.
Parker leaves the Liberty Stadium after making 157 appearance and scoring 29 tries since his move from the Celtic Warriors in 2004.
He has found recent game time hard to come by due to the form of the likes of Andrew Bishop, Ashley Beck and Tom Isaacs but he leaves the region with plenty of silverware having helped the Ospreys to three Celtic/Magners League titles and to victory over Leicester Tigers in the 2008 EDF Energy Cup Final at Twickenham.