By Joshua McElwee and Elizabeth Pineau

PARIS, Sept 26 (Reuters) - Crowds stretched the length of the Avenue des Champs-Élysées in Paris on Saturday, as Pope Leo urged Catholics to find happiness in faith, not material things, at the biggest event of his visit to France, an ‌outdoor Mass with an estimated 800,000 people.

Chants of "Leo, Leo" and "Long live the Pope" echoed down the roughly 2 km (1.2 miles) tree-lined boulevard, from ‌the Place de la Concorde to the Arc de Triomphe, as people pressed against security barriers for a glimpse of Leo as he arrived in an open-top popemobile.

The vehicle paused frequently as people ​waved white and yellow Vatican flags and Leo blessed people with disabilities, children and babies passed forward by volunteers.

Attendees included Brigitte Macron, the French president's wife, far-right leader Marine Le Pen, who is leading in the poll...