Ancelotti looked set to make a tough decision over whether to start Courtois or Andriy Lunin for Saturday's showdown at Wembley.
In Courtois's absence, Lunin has been a reliable performer for Los Blancos this season, establishing himself in the starting lineup ahead of Kepa Arrizabalaga.
Lunin has featured in all six of Real Madrid's Champions League knockout games, including the quarter-final second leg against Manchester City.
The Ukraine international made two saves in the penalty shootout to deny Bernardo Silva and Mateo Kovacic, helping Real Madrid progress to a semi-final against Bayern Munich.
Ancelotti confirms Courtois inclusion
However, Lunin has appeared in just four of Real Madrid's last five matches since Courtois returned from an anterior cruciate ligament injury.
The Belgian shot-stopper has shown no ill effects of his long injury layoff, keeping clean sheets against Cadiz, Granada, Alaves and Real Betis.
Having been left to ponder over his starting goalkeeper, Ancelotti's decision has ultimately been taken out of his hands.
Earlier on Friday, Lunin revealed that he would not start against Dortmund after struggling with illness in the lead-up to Saturday's final.
Ancelotti has now confirmed that Courtois will line up between the posts to make his first Champions League appearance since May 2023.
"Lunin has had flu, he hasn't been able to train," Ancelotti told reporters at Friday's pre-match press conference. "He'll travel tomorrow. He'll be on the bench, so Courtois will play."
Courtois set to return to Champions League stage
Courtois may be set to make his first European appearance of the season, but the pressure should not intimidate the experienced goalkeeper.
The 32-year-old has featured in 75 Champions League matches during his career, including a couple of final appearances.
As an Atletico Madrid player, Courtois experienced disappointment in the 2013-14 final, conceding a stoppage-time equaliser against Real Madrid before going on to lose 4-1 after extra time.
However, he finally got his hands on the trophy in 2021-22 when Real Madrid claimed a narrow 1-0 victory over Liverpool.
Courtois will now hope that he can help Los Blancos claim their 15th European crown in Saturday's clash with Dortmund.
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