The event, now in its 131st year, celebrates the region's heritage, more than 20 years after the closure of the last local pit.
Banners from the former colliery villages were paraded through the city, as brass bands played.
Labour leadership contender Jeremy Corbyn and trade unionists addressed a rally at the racecourse.
Liz Kendall, another candidate for the Labour leadership, and artist Grayson Perry were also among those taking part in the parade.
Tens of thousands of people, including former pit workers, have attended the Durham Miners' Gala.