Having won the Heineken Cup last weekend, Wilkinson's side, who had not been French champions since 1992, went on to take revenge for their defeat in the domestic final to the same opponents last year.
It was meant to be all about Wilkinson, with "Merci Jonny" stitched into all the Toulon team shirts, and that was the way the night unfolded in a packed Stade de France, with the black and red army occupying the south end of the stadium and the public address system playing God Save The Queen at the end.
"I would like the thank the whole team, the crowd but also Castres and all the other teams in the Top 14. I don't have the words, can't thank the French public enough," Wilkinson said.
"Thank you for all the memories. I have spent more than half my life with a rugby ball, it's going to be a big change."
Wilkinson scored four penalties and a drop goal before Delon Armitage sealed victory for Toulon with eight minutes left.
Castres' points came from Rory Kockott's boot and a try from Scotland's Max Evans.
A Wilkinson penalty put Toulon ahead, only for the defending champions to open a 7-3 lead when Evans scored an 80-metre touchdown after following up his own kick.
Kockott added the extras but Wilkinson sent over two penalties and a 23-metre drop goal to put his side just ahead at half-time.
Toulon opened a five-point lead early in the second half when Wilkinson curled a fine penalty between the posts from a tight angle.
With eight minutes left, another penalty for Toulon on the left side of the pitch was left to Armitage, who duly delivered to put them out of beyond reach.
Wilkinson, 34, made his Test debut in 1998 at the age of 18, becoming England's second-youngest international, with his second Test a 76-0 thrashing at the hands of Australia in the so-called "Tour of Hell".
From that inauspicious start he went on to play 91 Test matches for his country, despite suffering a number of serious injuries, helping them to the 2003 World Cup title and the runners-up spot four years later.
Wilkinson played six Tests for the British & Irish Lions, and is the second-highest Test points scorer behind New Zealand's Dan Carter with 1246.
Noted for his unique kicking stance that was later replicated by players around the world, he was deadly in front of the posts and unflappable in the most highly-charged of match situations, never more so than the 2003 World Cup final against Australia in Sydney.
While he did not like to be defined by his drop goal in the last minute of extra-time that won England their first and only world championship, it is undoubtedly the image that comes to mind for rugby fans the world over.