Giovanni was the youngest of his generation of Belfreys, the last son of Bartholomew and Antoinette. His family had a rather strict upbringing, but he managed to stray away from his father's supremacist ideals - unlike some of his siblings - and chose to live the liberal life. He was aware of how much wealth the Belfreys possessed, and so he was spoiled as a child - used to getting what he wanted, and always having a servant around to assist him. He'd later learn that this would impair him out in the real world, where no one will fend for him except for himself, but let's not get too ahead of ourselves, shall we?
Giovanni showed his first signs of magic at age 9, when he accidentally burned the tip of his brother's broomstick out of frustration while they were playing Quidditch. Because of this, he was enrolled at Hogwarts at age 11 where he was placed under Slytherin house. Naturally, his love for Quidditch manifested during his school years, and he played for the team as a beater beginning in his sophomore year. He continued playing until he was promoted to team captain when he was a fifth year - a title that he kept until graduation. Because of his skills, it wasn't long until he was hotly recruited by professional Quidditch teams all over Great Britain. He ultimately chose to go with the Montrose Magpies - one of the most successful teams in the league.
It was during his first few years with the Magpies that he met Nicole Oberlin, one of his teammates. As a natural flirt, Giovanni put the moves on and tried to seduce her. They ended up having a drunken one night stand which resulted in Nicole becoming pregnant. This ruined the plans she laid out for her life, and she was forced to quit the team without telling Giovanni, who was otherwise clueless and just brushed off Nicole's disappearance, not really caring. When Giovanni turned 21, he was recruited to join the British National Quidditch Team, something that he would be proud of for the rest of his life. He played in the international level for about three years, amassing great success, before going back to the Montrose Magpies after he's grown weary. He continued to play professional Quidditch until he was 26, when he suffered a grave injury during their finals match against the Ballycastle Bats. It was technically not career-ending, but figuratively, it was for Giovanni, who decided that it was time to retire after playing for so many years. He realized that he hasn't really done anything with his life other than to play Quidditch, and so he started looking for something more to do.
He travelled around the world for a year, treating it as a well-deserved break from the world of sports. Afterwards, having developed some sort of expertise over broomsticks because of his Quidditch experience, Giovanni got into the study of other forms of magical transportation. He started doing research on the Floo network, and Portkeys, as well as Apparition, and at age 28, he got a job in the Ministry of Magic. He never expected to have a career as a ministry man, but he felt at home in the Department of Magical Transportation, and worked hard because he loved it. Of all the wealth he's amassed from playing Quidditch, not to mention his own family's riches, Giovanni needed not to work anymore in order to sustain himself until his hair is gray because he'd have enough money, but he figured that life would be boring that way and he'd rather be doing something productive - that could help wizardkind - than sit around all day.