Barclay didn't feature for almost two months after suffering a hamstring injury but has played in every one of Glasgow's fixtures since returning at the start of February.
And he grabbed his first try of the RaboDirect PRO12 season in the dying moments of Glasgow's 51-24 defeat of Munster to retake top spot in the table ahead of Leinster.
Barclay didn't add to his 41 caps for Scotland during the season because he wasn't fit enough but Glasgow head coach Townsend believes he is currently playing better than ever.
"John's running lines were excellent, he worked well with Ruaridh (Jackson) and he picks his lines very well," said Townsend. "His timing was good so he's always at pace when he takes the ball and I thought that was his best game of the season.
"John is back to the form he showed when he was playing for Scotland. He scored a cracking try against Castres in the Heineken Cup but did his hamstring, so he wasn't fit enough for the Six Nations, but I'm really pleased for him."
Extensive in-game highlights of the RaboDirect PRO12 are now available on the official YouTube channel
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