The French probably invented braces. They wore strips of ribbon fixed into buttonholes called "bretelles" around the time of the French Revolution. Napoleon had a pair decorated with bumblebees, a symbol of his native Corsica
Benjamin Franklin, publisher, diplomat, framer of the Declaration of Independence and the U. S. Constitution, inventor of the lightning rod, the Franklin stove, and bi-focal glasses also adapted and made popular "gallowses" or suspenders around 1736. He made them part of the uniform of the Nation’s first volunteer fire dept in Philadelphia. "Why do firemen wear red suspenders?" The inspiration for gallowses probably came from gallows, which is also a method of hanging things.
The first gallowses had an H-back, and then in the 18th century they crossed over in an X-back, and finally around 1850 arrived at the forked Y-back still in style today.
The first patent ever issued for modern suspenders - the kind with the familiar metal clasp - was issued to an inventor called Roth (US patent # 527887 issued in October, 1894.)
Original braces were made of silk or satin and fastened to trousers with buttons. They were also very ornate, often embroidered by a sweetheart. Debussy’s braces were floral patterned, Napoleon’s had his personal bee insignia and Queen Victoria gave Disraeli a pair with foxhunting scenes. Even Franklin D. Roosevelt had a pair bearing flags and eagles.
The hot summer of 1893 drove men to give up their braces and opt for belts. The trend continued and the popularity and acceptability of belts increased. At the beginning of the 20th century very few dress trousers were made with belt loops, today few are made without them.