Spaniard Alcaraz, who triumphed at the same venerable London championship a few weeks before claiming his first Wimbledon title in 2023, extended his winning streak to 18 matches but was pushed hard by Lehecka who underlined his own credentials as a rising force.
Alcaraz, 22, pounced at 5-5 to break the Lehecka serve and duly bagged the opening set in 45 minutes in Sunday's final.
Lehecka, bidding to become the first Czech to win the Queen's title since Ivan Lendl in 1990, continued going toe-to-toe with the five-times grand slam champion and edged the second-set tie-break with some clinical tennis.
Alcaraz had more in his locker though and forged 4-1 ahead in the decider as Lehecka's level finally began to drop on a breezy Andy Murray Arena.
He then broke the 23-year-old Lehecka's serve again to complete victory, letting out a roar of a delight as Lehecka struck a backhand into the net.
While Alcaraz will be seeded No.2 at Wimbledon behind Jannik Sinner as he bids for a hat-trick of titles there, he will arrive in red-hot form and as overwhelming favourite.
He has won 27 of his 28 matches since April, his lone loss coming against Holger Rune in the Barcelona final, and Sunday's win was his fifth title this year.
"This is really special this trophy and this tournament for me," Alcaraz said on court as he clutched the huge piece of silverware.
"Jiri had an incredible week and his level is very high and it's a nightmare to play against you," he added, to his opponent.
Lehecka, whose ball-striking and physique are not dissimilar to Lendl's, beat home favourite Jack Draper in the semi-finals on Saturday and began full of confidence against Alcaraz whom he beat at the start of the year in Doha.
With serve dominating on the slick lawn, there was nothing between the players until Lehecka made a couple of errors at 5-5 and Alcaraz needed no second invitation to take the set.
The second set followed a similar pattern but it was Lehecka who raised his game in the tiebreak to get a mini-break ahead.
Alcaraz replied to win a sensational point at 3-4, sprinting to retrieve a drop shot and then back to chase down a lob.
But Lehecka did not flinch and banged down an ace. Alcaraz double-faulted at 5-5 and then Lehecka levelled the final.
Lehecka was unable to carry that momentum though and Alcaraz quickly re-established control and surged to victory.
"The goal this week was just to compete and have a few matches on the grass and this final was a gift for me," Alcaraz said.
"I just enjoyed the moment and the final, I felt like I was in control most of the time."
