The 33-year-old Ireland international moves to Glasgow until at least May 2016, after spending the last two seasons at Munster.
A Churchill Cup winner with Ireland in June 2009, James began his career at Leinster before moving to Connacht and then Munster.James Downey will join Glasgow from Munster
Prior to joining Munster for a second spell in 2011, he spent a season at Calvisano in Italy before moving to Northampton Saints.
He quickly became a regular in the Saints backline at inside centre, making 148 appearances and scoring 13 tries during a five-year spell at Franklin's Gardens. In 2009 he won the European Challenge Cup with Northampton.
James made 47 appearances for Munster and has featured in all of their Heineken Cup games over the past two seasons, including the quarter-final win over Toulouse at Thomond Park in April.
He recently faced the Warriors at Scotstoun, after being included in Rob Penney's starting line-up for the RaboDirect PRO12 Play-Off in May.
James made his senior debut for Ireland when he started against Canada on the tour to North America last summer.