Aboubacar Cherif Keïta scored the decisive goal in the 38th minute, giving Guinea their first title in the modern edition of the regional competition, which began in 2018.
The victory also provided revenge for Guinea, who had previously lost to The Gambia during the group stage of the tournament.
Keïta delivers decisive moment
The final was closely contested, with both teams determined to finish their impressive campaigns with the trophy.
Guinea eventually broke the deadlock in the 38th minute when Keïta showed excellent control to bring down Morlaye Sylla's corner before firing into the net.
The goal proved decisive as Guinea defended their advantage throughout the remainder of the encounter, resisting The Gambia's attempts to find an equaliser.
The Young Scorpions pushed for a response but could not break down Guinea's organised defence.
Guinea overcome defending champions Senegal
Guinea's triumph followed an impressive campaign in Bamako, where they also defeated tournament favourites and defending champions Senegal in the semi-finals.
The Guineans produced a remarkable comeback after falling two goals behind, eventually eliminating Senegal after extra time.
They also recorded important victories against hosts Mali and Liberia during the group stage.
Their only group-stage defeat came against The Gambia, making Friday's final victory particularly significant.
Both finalists qualify for 2027 U-20 AFCON
Although The Gambia finished as runners-up, both finalists achieved their primary objective by securing qualification for the 2027 U-20 Africa Cup of Nations in Ghana.
Guinea will return to the continental tournament for the first time since 2017, when they finished third at the competition in Zambia.
The Gambia will also be back at the finals after missing the 2025 edition. The Young Scorpions previously finished runners-up in 2023 and third in 2021.
The qualified teams will now turn their attention to preparing for the continental competition in Ghana next year.
A historic achievement for Guinea
The triumph represents a significant milestone for Guinean youth football, ending the country's wait for a WAFU-A U-20 title in the modern competition.
It also provides encouragement ahead of the 2027 U-20 AFCON, where Guinea will hope to build on their regional success and compete strongly against Africa's leading youth teams.
For The Gambia, the runners-up finish confirms their continued competitiveness at youth level and offers another opportunity to challenge for continental honours next year.
Match details
• Competition: WAFU-A U-20 Championship 2026
• Final: Guinea 1-0 The Gambia
• Date: Friday, 30 October 2026
• Venue: Mamadou Konaté Stadium, Bamako, Mali
• Goal: Aboubacar Cherif Keïta 38'
• Champions: Guinea
• Runners-up: The Gambia
• 2027 U-20 AFCON qualification: Guinea and The Gambia