Having beaten Brazil 45-0 on Wednesday, Uruguay claimed the South American U19 Championship at the Estadio Charrúa in Montevideo with a 29-11 win over Chile this weekend.
Despite the defeat, Chile finished second in the round-robin tournament thanks to a 52-14 win over Paraguay in the opening round.
As regional champions, Uruguay will now take their place in the line-up for World Rugby U20 Trophy 2020, to be played in Valencia, from 14-27 September, joining hosts Spain and relegated World Rugby U20 Championship team Scotland. The five other regional qualifiers have yet to be decided.
Winning the South American U19 Championship also confirmed Uruguay's place, along with runners-up Chile, third-place Paraguay and Argentina, at the newly-formed Americas Rugby U20 Championship next year, while Brazil, who finished bottom of the standings, will participate in the second-tier Americas Rugby.
Inaugural Trophy champions in 2008 and tournament regulars since then, Uruguay's participation looked under threat as Chile dominated the early stages of the decisive match.
Los Teritos overcome slow start
Chile used their big forward pack to get on top and moved the ball well, and they were rewarded with an 11th-minute try for Benjamin Goni to add to an earlier penalty from the boot of Lucas Sandoval.
Slowly but surely Uruguay got a foothold in the match and Juan Vargas pulled three points back with the first of his five penalties.
Number eight Carlos Deus' 26th-minute try was converted by Vargas to hand Los Teritos the lead for the first time but Chile ended the half with the narrowest of advantages when Sandoval punished an indiscretion by Uruguay hooker Agustin Conserva which earned him a yellow card.
Three Vargas penalties in a 10-minute spell after the break reflected the shift in momentum before Uruguay put clear water between themselves and Chile with a try for Conserva, Varga converting to make it 26-11.
Any hopes Chile had of mounting a comeback disappeared when they lost two players to the sin-bin and Varga closed out the scoring with another penalty in the final quarter.
Replacement scrum-half Javier Fernández admitted qualifying for the U20 Trophy had been quite a journey.
"It was a long process that began six months ago and we know each other very well," he said. "That was a key aspect. We are very happy to be going to the Trophy next year."
A try nine minutes from time secured Paraguay a 22-17 win over Brazil in the match to decide third place.