Casteford Tigers missed out on lifting the Super League leaders’ shield after crashing to defeat in France.
Nathan Brown’s St Helens needed just one point from their final two league games to secure the title, but were well beaten by Warrington last week and lost a thriller to Huddersfield on Friday.
Consequently Castleford - 200-1 outsiders at the start of the season - kicked off away to Catalan Dragons on Saturday knowing the shield would be going back to Yorkshire if they won by any margin.
They fluffed their lines, though, and were beaten 28-6, ending the season in fourth.
It is the first silverware St Helens have won since their move to Langtree Park and they will get an immediate chance to show it off to the Tigers, with the pair to meet in the first round of the play-offs next weekend.
In the Championship play-offs, Sheffield ended the challenge of Batley after some late pressure saw the Eagles claim a 16-0 victory.
The Bulldogs escaped relegation from the second tier with victory over Doncaster on the final day of the league season last week.
Despite resisting for over an hour, Batley eventually succumbed to the defending champions, who finished fifth in the table and have now advanced to week two of the play-offs.
Neither side could make any breakthrough until the 64th minute, when Dominic Brambani finally got the first points on the board with a penalty.
Etu Uaisele scored a try five minutes later although Brambani’s failure to add the extras meant the game was still very much alive heading into the final 10 minutes.
But it was the Eagles who dominated in the closing stages as Quentin Lauulu-Togagae’s converted try doubled Sheffield’s lead before Uaisele crossed the whitewash three minutes from time to make sure there was no way back for Batley.