Zacarías Ghailan was born in Barcelona on 28 June 2002 and came to FC Barcelona at the age of 14 from Damm. He started out in the U16B squad before moving up quickly through the age categories under coaches Franc Artiga and Óscar López, making his debut for the U19A side when he was still U19B team member.
In the season 2020/21 an injury kept Ghailan sidelined for the early part of the season but he recovered to play an important part of the U19A side's league title winning campaign and their run to the final of the Champions Cup. Zacarías joined the Barça B squad at the start of the 2021/22 season under coach Sergi Barjuan.
Zacarías Ghailan has dual Spanish and Moroccan citizenship and is a U20 international with Morocco having featured in the U20 African Cup of Nations in 2021 for the African side.