The 28-year-old signed for Glasgow in 2010 and has been a key member of the squad ever since, scoring a try in the triumphant 2015 PRO12 Final.
Just as comfortable playing in the back-row as he is in the second-row, Harley broke Graeme Morrison's club appearance record against Munster last season and will reach another milestone when he leads the team out on Sunday.
Ryan Wilson will also reach a personal milestone against Cardiff Blues playing his 150th game for the club.
Wilson and Harley both joined the Warriors at the same time and Harley made his debut coming on for Wilson against Leinster at Firhill.
Scott Cummings, Callum Gibbins and Matt Fagerson join the pair as the back-five of the scrum.
Oli Kebble and D'arcy Rae return to the starting XV as two of 11 changes to last weekend's defeat to Benetton. Grant Stewart once again starts at Hooker.
Brandon Thomson starts at fly-half outside of Ali Price and Nick Grigg comes in to partner Sam Johnson in midfield.
It's a brand new back-three with Stuart Hogg, DTH van der Merwe and Tommy Seymour all returning.
Glasgow Warriors Head Coach Dave Rennie said: "Rob and Ryan are both bloody good men who are really passionate about this club.
"They're good quality people and are highly respected within the group. It'll be a special day for them and their families.
"Obviously the last three weeks have been disappointing, but we've created a lot of opportunities in those games and just haven't been as clinical as we've needed to be and the quality of our decision making hasn't been good enough.
"It's hurt us but there's no sense of panic, we need to be sharper and we know this is a massive game for us in the context of Europe and we've picked the side accordingly."
15 Stuart Hogg
14 Tommy Seymour
13 Nick Grigg
12 Sam Johnson
11 DTH van der Merwe
10 Brandon Thomson
9 Ali Price
1 Oli Kebble
2 Grant Stewart
3 D'arcy Rae
4 Robert Harley
5 Scott Cummings
6 Ryan Wilson (Co-Captain)
7 Callum Gibbins (Co-Captain)
8 Matt Fagerson
Substitutes
16 Kevin Bryce
17 Alex Allan
18 Petrus du Plessis
19 Tim Swinson
20 Chris Fusaro
21 George Horne
22 Adam Hastings
23 Lee Jones
Players unavailable through injury: Fraser Brown (knee), Alex Dunbar (thigh), Zander Fagerson (ankle), Jonny Gray (shoulder), Siua Halanukonuka (calf), Peter Horne (knee), Nikola Matawalu (illness), Robbie Nairn (knee) and George Turner (ankle)