As Glasgow beat Ulster at Scotstoun to top the table and then repeated the feat last Friday night to reach the final, the 25-year-old flanker did not feature at all.
However, Townsend has called on Harley for the big occasion as the Warriors prepare to take on Munster in Belfast this evening and, with plenty of back-row options at his disposal, the coach is confident he has made the right call.
"We felt this was a good game for Rob Harley to play in," said Townsend. "Rob has, over the last three or four years, been one of the most consistent at the club.
"His form hasn't been at the level he would like it to be over the last three or four games but having had a couple of weeks to work on a few things we think this will be a perfect game to bring him back in.
"With an extra day's preparation there was good opportunity for us as coaches to have a really good think about what our best team would be and there are going to be players that have been very unlucky not to be selected. Adam Ashe is one of them and Pat MacArthur another."
Elsewhere, DTH van der Merwe takes his place on the wing after a star showing last week, with Niko Matawalu dropping to the bench.
The 29-year-old, who will join Scarlets next season, grabbed the dramatic match-winning try against Ulster and Townsend admits he has eared the opportunity.
He said: "What an impact DTH made last week. He was in great form before he broke two bones in his hand. He has fought very hard to get back into the squad and he has earned his place in the team.
"There was no more important try for his club than last week and if he could score one that's even more important, we will be a happy bunch after the game."
This is Glasgow's second consecutive appearance in a PRO12 Final, following last year's 34-12 defeat to Leinster at the RDS.
The previous season saw a play-off defeat, while this year was the first time they have finished top of the regular-season table as the club's upward trajectory continues.
"I believe the reasons we lost were more to do with emotional control than anything technical or tactical," recalled Townsend.
"We played some really good rugby, we got in behind Leinster on two or three occasions but we just rushed things a bit.
"We played really well and trained really well but maybe we just got a bit excited at times. There is a calmness about the group and in the coaching staff - that was our first final as well so we have learned a lot - but we are going to be challenged out there."
And while club captain Al Kellock, who will retire after the final, is replaced by Leone Nakarawa in the second row, the boss is excited to call on his services at some point this evening.
"We see Al having a big influence on this game," added Townsend. "He has been great in the preparation and we know, whether it's the last 20, 30 or whatever minutes of the game, to have his presence will really help us."
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