Ben Youngs and Billy Twelvetrees were the try-scorers while Jeremy Staunton kicked two conversions on an eye-catching debut for the club.
The game brought to an end a summer training camp in Saint-Affrique where they have been based for the last week as Richard Cockerill’s squad builds towards the start of the Guinness Premiership campaign next month.
Summer signing Staunton made his first start in a Tigers shirt at fly-half and there was a return to action for Richard Blaze after a nine-month absence with a foot injury. Anthony Allen was a late inclusion at the expense of Dan Hipkiss, with the side captained by Ben Kay.
The game kicked off in front of a large crowd enjoying the warm evening sunshine in the south of France.
Castres took an early lead with a try through lock Rodrigo Capo Ortega. Flanker Ibrahim Diarra was well tackled just short of the tryline, but the ball was returned on the French side and Capo Ortega found a gap down the side of the ruck to score. Cameron McIntyre added the conversion.
Fly-half McIntyre then kicked a penalty in front of the posts on 12 minutes to put Castres 10-0 ahead.
Drives by George Chuter and Jordan Crane took Tigers deep into Castres territory and triggered the visitors’ first period of pressure – and their first points.
They forced an attacking lineout and had the Castres pack back-pedalling with a driving maul which was illegally stopped eight metres out. Tigers opted for the scrum and, with another strong platform, Crane popped off the back to send Ben Youngs over on the right. Staunton’s conversion left Tigers 10-7 behind after 23 minutes.
Good work by Matt Smith and Scott Hamilton made a threatening break on the left but then Castres wing Matthieu Nicolas counter-attacked on the opposite wing where Johne Murphy was alert to the danger.
Another close-range McIntyre penalty extended the Castres lead to 13-7 at half-time.
Tigers took the lead with their second try shortly after the restart. Staunton made an explosive break on halfway and was supported by Twelvetrees who held off a couple of defenders to score. Staunton’s conversion edged Tigers 14-13 ahead.
McIntrye was on target with his fourth kick from four to reclaim to lead for the French side moments later.
Murphy and Staunton then made excellent breaks to turn the Castres defence before Allen was forced to defend near his own line to thwart a counter-attack.
Replacement Romain Teuulet then kicked another Castres penalty to put them 19-14 up.
It was a hugely entertaining game, helped by Tigers opting for lineouts and scrums when presented with kickable penalties and looking to run the ball from deep.
With Craig Newby off the field, Castres replacement Paul Bonnefond took advantage of the extra man to cross in the left-hand corner for the final score of the game.
Tigers return to action against Nottingham at Meadow Lane next Saturday (4pm).
Tigers: J Murphy, Smith, Twelvetrees, Allen, Hamilton, Staunton, Youngs; Stankovich, Chuter, Castrogiovanni, Blaze, Kay (c), B Deacon, Woods, Crane. Reps: Davies, Ayerza, White, Cole, Parling, Hemingway, Green, Newby, Pienaar, Grindal, Tonks, Forsyth, Cobden, Hurrell
Castres: Bourret, Nicolas, Audin, Cabannes, Andreu, McIntyre, Tillous-Borde; Hoef, Bonello, Coetzee, Michaux, Capo Ortega, Diarra, Masoe, Nell.
