Macleod is joined in the starting lineup with Wales international teammate Eddie James, who has recovered from a long-term back issue.
Open-side flanker Macleod, who started both Wales’ summer Tests against Japan, has not played since suffering a pectoral muscle injury against Munster on the opening weekend of the United Rugby Championship.
New signing Fletcher Anderson will also make his first appearance for Dwayne Peel’s side at number eight in the fixture after arriving from Crusaders in New Zealand at the start of the month.
Peel has named a strong squad in preparation for the resumption of URC action at home to Glasgow Warriors a week on Saturday, with a 28-strong group heading to West London.
Ellis Mee, Jac Davies and Tomi Lewis make up an attacking back three. In midfield, James combines with fellow Wales international Johnny Williams. Sam Costelow and Gareth Davies provide an experienced partnership at half-back.
The front row consists of Kemsley Mathias, Marnus van der Merwe and Archer Holz, while Dan Gemine packs down alongside Sam Lousi in the second row.
Anderson starts at number eight in a back-row that also contains Macleod and Jarrod Taylor.
A 13-man bench includes 17-year-old Wales U19s fly-half Carwyn Leggatt-Jones, who is set for his Scarlets senior debut and second row Kai Jones, another who played for Wales U19s in Paris last weekend.
Scarlets team to play Harlequins, Friday, November 21
15 Ellis Mee; 14 Jac Davies, 13 Johnny Williams, 12 Eddie James, 11 Tomi Lewis; 10 Sam Costelow, 9 Gareth Davies; 1 Kemsley Mathias, 2 Marnus van der Merwe, 3 Archer Holz, 4 Dan Gemine, 5 Sam Lousi, 6 Jarrod Taylor, 7 Josh Macleod (captain), 8 Fletcher Anderson.
Replacements: 16 Harry Thomas, 17 Sam O’Connor, 18 Henry Thomas, 19 Kai Jones, 20 Osian Williams, 21 Dane Blacker, 22 Carwyn Leggatt-Jones, 23 Macs Page, 24, Ioan Nicholas, 26 Ben Williams, 27 Gabe McDonald, 29 Josh Morse, 30 Harri O’Connor.
[Lead image: Scarlets Rugby]
