It became popular in Europe after Queen Victoria wore a white lace dress when she married Prince Albert in 1840, primarily to show support for the handmade lace industry in England which had been damaged by the rise of machine-made lace. Victoria’s twelve bridesmaids also wore white.
In 1849, Godey’s Lady’s Books said, “Custom has decided from the earliest ages, that white is the most fitting hue, whatever may be the material. It is an emblem of the purity and innocence of girlhood, and the unsullied heart she now yields to the chosen one” but making white symbolic of purity or virginity was a more recent attribution, not something “from the earliest ages”.
White didn’t become a popular wedding dress color in the U.S. until the 1860s, and then it was still only for those who could afford it since it was difficult and expensive to make a truly white cloth and, before dry-cleaning, or even reliable bleaches, it was an impractical color to keep clean.
Brides had worn white before but they also wore many other colors, depending on their wealth and status and what ways the gown would need to be repurposed for later.
See History of Wedding Dresses and Queen Victoria’s wedding, or why modern brides wear white for more information.