From pole position, Marciello was never seriously threatened at the head of the field over the course of the 16-lap race, ultimately winning by a comfortable margin of 2.5 seconds in his Team Landgraf Mercedes-AMG GT3.
It means the Italian/Swiss driver becomes the first repeat winner of the FIA GT World Cup since its inception in 2015, also taking a final win as a factory Mercedes GT driver before his expected departure to BMW.
Four-time Macau GT winner Edoardo Mortara was second at the wheel of his Absolute Racing-run Audi R8 LMS GT3, while the podium was completed by Augusto Farfus in the Rowe Racing BMW M4 GT3.
It was Maro Engel who spent the early part of the race as Marciello's nearest pursuer, with the top three staying in grid order at the start.
The order didn't change until the safety car was deployed on lap eight, the result of Weian Chen burying his Ferrari 488 GT3 in the barriers at Lisboa.
But immediately before the race resumed on lap 10, Engel slowed dramatically with gear selection trouble, giving Marciello a near-three second cushion for the restart that he was able to manage until the chequered flag.
All eyes were then on the battle for second between Mortara and WRT BMW man Sheldon van der Linde, who had climbed one place from fifth on the grid at the original start.
That battle was defused when van der Linde pitted at the end of lap 11 after picking up a puncture, promoting brand stablemate Farfus to the final podium position.
Fourth went to the sole Ferrari 296 GT3 of Daniel Serra, who set the fastest lap of the race.
Dani Juncadella moved up from ninth on the grid to complete the top five in his Craft-Bamboo Mercedes, followed by Laurens Vanthoor in the best of the Porsche 911 GT3 Rs on a weekend to forget for the Stuttgart marque.
Christopher Haase was seventh for Audi, while the top 10 was completed by three more Porsche drivers, with Alessio Picariello heading Earl Bamber and Chinese racer Leo Ye Hongli.
Kevin Estre was running in ninth in the closing stages when he appeared to hit the wall at Fisherman's Bend, dropping him down to 12th.
Macau FIA GT World Cup - race results:
| Pos. | No. | Driver | Car | Laps | Time | Delay |
|---|---|---|---|---|---|---|
| 1 | 48 | Raffaele Marciello | Mercedes | 16 | 38'35.554 | |
| 2 | 40 | Edoardo Mortara | Audi | 16 | 38'38.064 | 2.510 |
| 3 | 11 | Augusto Farfus | BMW | 16 | 38'39.849 | 4.295 |
| 4 | 51 | Daniel Serra | Ferrari | 16 | 38'41.572 | 6.018 |
| 5 | 91 | Daniel Juncadella | Mercedes | 16 | 38'42.069 | 6.515 |
| 6 | 99 | Laurens Vanthoor | Porsche | 16 | 38'43.350 | 7.796 |
| 7 | 41 | Christopher Haase | Audi | 16 | 38'43.931 | 8.377 |
| 8 | 15 | Alessio Picariello | Porsche | 16 | 38'44.490 | 8.936 |
| 9 | 22 | Earl Bamber | Porsche | 16 | 38'48.726 | 13.172 |
| 10 | 33 | Leo Ye Hongli | Porsche | 16 | 38'49.489 | 13.935 |
| 11 | 120 | Matteo Cairoli | Porsche | 16 | 38'50.359 | 14.805 |
| 12 | 27 | Kévin Estre | Porsche | 16 | 38'51.839 | 16.285 |
| 13 | 13 | Cong Fu Cheng | Audi | 16 | 38'55.380 | 19.826 |
| 14 | 2 | Jules Gounon | Mercedes | 16 | 39'08.008 | 32.454 |
| 15 | 28 | Thomas Preining | Porsche | 16 | 39'34.702 | 59.148 |
| 16 | 32 | Sheldon van der Linde | BMW | 16 | 39'34.841 | 59.287 |
| 17 | 70 | Marchy Lee | Mercedes | 16 | 39'41.329 | 1'05.775 |
| Ret | 77 | Maro Engel | Mercedes | 10 | 25'38.861 | - |
| Ret | 52 | Weian Chen | Ferrari | 7 | 16'15.899 | - |
