Fin introduced themselves by their new name before reading a bible verse to the congregation at Christ Church United Methodist in Charleston.
The teen wore a black pantsuit and buzz-cut hairstyle, after previously being pictured with their new short cropped hair as early as February this year.
Jennifer Garner and Ben Affleck 's 15-year-old has been pictured for the first time since revealing their new name, Fin
Formerly known as Seraphina Rose, the teen made their first official appearance as Fin at a memorial service for Jennifer's father last weekend
The funeral was the first time the top actors' kid introduced themselves in public with a new name.
The memorial service, streamed live on was for Jennifer Garner's father William Jack Garner, who died a week earlier age 85.
Following William's other grandchildren, Fin introduced themselves at the church lectern saying: 'Hello my name is Fin Affleck,' then read Chapter 16, Verse 8 from the Book of Proverbs: 'Better is a little with righteousness, than a large income with injustice.'
Fin's mom Jennifer announced Billy's death on in a heartbreaking post last Monday, saying he passed away 'peacefully'.
'We are grateful for Dad's gentle demeanor and quiet strength. For how he teased with a mischievous smile, and for the way he invented the role of all in, ever patient girl dad. We are grateful for his work ethic, leadership and faith,' she wrote.
Fin is Garner and Affleck's middle child, with an older sister Violet Anne, 18, and younger brother Samuel, 15.
Their parents split in 2015 and finalised their divorce in 2018, but maintain a friendly relationship.
In 2022 Affleck married singer Jennifer Lopez, whose 16-year-old daughter Emme Maribel Muniz and has become close with Fin as a step-sibling.