The 36-year-old is set to make his 632nd appearance in the top flight on Saturday as the Baggies prepare to face West Ham United.
He made his Premier League debut for Aston Villa in May 1998 and returned to the Midlands this summer, joining Albion from Everton, and Pulis says he has been a great servant.
"It is a wonderful achievement, we have only just had him a few weeks," said Pulis.
"I have always rated him as a player but you don't realise how good he is until you actually work with him."
"Managers who have had him for longer periods are better versed talking about Gareth than myself."
Barry reportedly cost West Brom just £800,000 as he made the switch from Everton in the summer.