Braga are on the rise, having played in the group stages of the Europa League in seven of the last eight seasons. They played in the final of Europe's secondary club competition in 2011, losing 1-0 to FC Porto.
Braga are currently third in the Portuguese Primeira Liga.
Since buying PSG in 2011, QSI have transformed the fortunes of the Parc Des Princes outfit, winning 29 trophies in that time and becoming a major force in European football.
They will be hoping to do something similar with Braga after acquiring a 21.67 per cent share in the club.
QSI chairman and PSG president Nasser Al-Khelaifi said: "Qatar Sports Investments is proud to invest in leading sports businesses and brands around the world, enabling them to reach their full potential.
"Portugal is a country founded on football – with some of the most passionate fans and one of the best talent systems in the world.
"SC Braga is an exemplary Portuguese institution – with a proud history, enormous ambition and a reputation for excellence on and off the pitch.
"As an investor and partner, we look forward to the club innovating, growing and developing further – across the men's and women's teams, on the commercial and brand side, and across all the communities and businesses it supports – as SC Braga continues its ambitious path."
Braga president Antonio Salvador added: "Braga is delighted to welcome Qatar Sports Investments as an investor in our club.
"We believe that this is the right shareholder to accelerate our growth and expansion, helping us deliver on our amazing potential as a club.
"The extraordinary experience of Qatar Sports Investments – with its global expertise, acumen and a track record of amazing results across sport and business – will bring enormous value and help us deliver on our ambitious plans.
"It is a great day for our club, our fans and our city, as we look forward to many future successes for SC Braga."
