Camilli moved into the lead on SS2 after an early battle with title-chaser Mads Østberg’s similar Citroën C3 Rally2.
A puncture for Østberg on Friday afternoon gifted Camilli the chance to stretch his legs and he steadily increased his advantage over the remaining two days.
The Frenchman played it safe with two spare wheels on board for most loops whilst wet conditions on the final stage caused a few hairy moments, but he continued to set fastest times until the end to win by 20.2sec.
"I put the rain set-up on for the final stage but I was really struggling at the start because there was no rain, so I thought I made a mistake,” explained Camilli. “At the end it was very slippery, but I took some risks and we are very happy."
Whilst Camilli won the rally, results elsewhere meant the absent Mikkelsen was crowned the drivers’ champion.
The Norwegian had planned to end his season at FORUM8 ACI Rally Monza next month, but as neither Østberg nor Teemu Suninen scored enough points to catch him, the title was decided earlier than anticipated.
“It's super weird to suddenly become champion,” Mikkelsen said from the Salou service park. “It's really nice now to go to Monza without any pressure and just go for it.”
Suninen took second on his Hyundai i20 N Rally2 debut. The Finn bagged a handful of stage wins despite his limited experience with the car and even suggested he may be back with the Hyundai squad for Monza.
Erik Cais also had a debut to remember. The Czech driver steered his Ford Fiesta Rally2 to numerous stage wins to end his maiden WRC outing 56.1sec behind Suninen in third. Østberg was 55.7sec further back after a soul-destroying weekend, blighted by two punctures and suspension troubles.
American pilot Sean Johnston brought his C3 home 3min 39.0sec behind Østberg, whilst Georg Linnamäe completed the leaderboard 6min 39.1sec back from the leaders in a Volkswagen Polo GTI R5.
Jari Huttunen was the only non-finisher. Engine issues plagued his Hyundai from the start and he eventually retired on Saturday lunchtime at service.