Ryan Hall dazzled for the six-time Super League champions with scores in either half as Leeds ran in four tries on their way to winning the prestigious competition for the 12th time.
Brian McDermott's Leeds side dominated proceedings at Wembley and were never behind in the match as Castleford struggled to find their momentum in their first Challenge Cup final since 1992.
Leeds, who had lost six finals since their last win in 1999, used their big-game experience to control the opening half and continually piled pressure onto the Tigers defence.
Tom Briscoe - a losing finalist with Hull FC 12 months ago - broke the deadlock within five minutes as Rhinos stretched the Castleford defence with quick hands to allow the winger to cross in the corner.
Castleford hit back, though, as Daryl Clark went over at the other end, having spun away from the challenge of Zak Hardaker.
Marc Sneyd missed the kick and Leeds quickly extended their two-point advantage as Danny McGuire collected an up-and-under kick before using his momentum to score.
Kevin Sinfield kicked his second conversion and, seven minutes later, had another opportunity with the boot as Hall flexed his muscles for the first time to score a third Leeds try.
Having received the ball on the left touchline, the winger bulldozed his way through two challenges on the Castleford line, but Sinfield was unable to add the extras as Leeds finished the half 16-4 ahead.
Castleford cut that deficit to six points early in the second half as Oliver Holmes capped off a flowing move by converting Michael Shenton's inside pass, with Liam Finn kicking the extra points.
Leeds took their time to get back up to full speed after the break, but Hall's second try gave them further breathing space.
Quick passing from the breakdown saw the ball end up with the winger and he escaped the attentions of four defenders to power his way over the line.
Sinfield's kick struck both posts before going over and a drop goal from McGuire with three minutes remaining completed the victory for Leeds.