Kai Havertz bagged a stoppage-time winner as The Gunners beat Sporting 1-0 in the first leg of their Champions League quarter-final in Lisbon.
Arsenal will take their lead to the Emirates next week where they will aim to defend a narrow lead in front of a home crowd whose Champions League dreams are only growing.
Dowman, aged just 16 years and 97 days, came on as a substitute in the 76th minute of Arsenal's win as he became the youngest-ever player to feature in a Champions League quarter-final.
He overtakes Barcelona star Lamine Yamal, who was 16 years and 272 days old when he played against Paris Saint-Germain in the 2023-24 quarter-finals.
This is yet another record for the teenager who, in March, he became the Premier League's youngest-ever scorer after a remarkable stoppage-time goal against Everton.
He has also become the youngest-ever Champions League player when he featured for Arsenal against Slavia Prague aged 15 years, 308 days.
The 16-year-old has a pre-agreement to sign his first professional Arsenal contract in December, when he turns 17 and fans will be hoping that he sticks to the agreement and commits his future to a side who have handed him so much opportunity so far.