Veganism is for me intricately linked to animal rights' movements. Vegetarianism can be argued to be okay, since it (theoretically) doesn't necessarily kill the animals involved in producing milk and cheese etc. What sparked off the vegan movement? Who were the initiators and what was their motivation for going vegan?
Vegetarianism has been around for a long time, but veganism not quite as long.
The earliest known vegan was Al-Maʿarri, an Arab philosopher from the late 10th century.
[His] diet was extremely frugal, consisting chiefly of lentils, with figs for sweet; and, very unusually for a Muslim, he was not only a vegetarian, but a vegan who abstained from meat, fish, dairy products, eggs, and honey, because he did not want to kill or hurt animals, or deprive them of their food.
(From the introduction of The Epistle of Forgiveness Or A Pardon to Enter the Garden)
His choice was based on being kind to animals and general health.
In the 19th century (the 1800s) veganism/vegetarianism (both) saw a large movement in favor of them. Percy Shelley published a paper named A Vindication of Natural Diet, supporting "abstinence from animal food and spirituous liquors". (aka beer and animal products)
Finally, the Vegetarian Society was founded in 1843. An article in the society's magazine in 1851 describes alternatives for leather though, implying that some more 'modern' vegans existed in the society though.
Donald Watson coined the word 'vegan' in 1944 and co-founded the Vegan Society.
In the 1960s and 70s, as you noted, a resurgence in the popularity of veganism/vegetarianism arose. Finally, in the 1990s - 2000s it became not unusual to be vegan/vegetarian, and the EU officially defined veganism as it relates to food in 2010.
TL;DR: early vegans were around from the beginning of the second millennium, and then it became more popular in the 1800s and later the 1970s.