Graham has propelled himself from outside the squad for the series, which will roll into home matches against Fiji, South Africa and Argentina, to the matchday 23 for Saturday’s November opener.
“He has shown great form over the last three or four games,” said Townsend of the Hawick youngster, who had been invited to train with the initial official 40-man pool.
“Darcy had played the week before [we announced the squad] against Montpellier [in the Heineken Champions Cup] and we were impressed so we said to him that, depending on what happens over the next three or four weeks and how you play, you could easily come into the mix for one of these games.”
Edinburgh hooker and skipper Stuart McInally will captain what is a Scots pro-team select due to the match falling outside the Test window. Winger Tommy Seymour will act as joint vice-captain along with his Glasgow skipper Ryan Wilson.