The advance is a blow to IS, which had been battling to hold onto the border town.
Analysts say it served as a primary conduit for incoming weapons and fighters, as well as for outgoing black market oil.
"It has been an IS stronghold for a while now, and it has been described as the gateway to Raqqa," said Charlie Winter, a researcher on jihadism at the London-based Quilliam Foundation.
"Certainly, it's of strategic importance because it's a border town through which equipment, recruits, et cetera, can pass."
Tal Abyad is 70 kilometres east of the Kurdish-majority town of Kobane, where Kurdish forces battled for months before expelling invading IS forces in January.
Mutlu Civiroglu, a Kurdish affairs analyst, said Tal Abyad was a financal and logistical hub for IS.
"Once you cut this hub it is going to be very hard for IS to smuggle in fighters, to sell oil and deal in the other goods they deal in," he said.
http://www.abc.net.au/news/2015-06-16/k ... te/6548316