Hood: Outlaws & Legends

Rank 100 requires 549,380 experience(I may be off by a little)

After each match the XP gathered from the match goes into a pool and is distributed to player and character level.

You can get XP from various actions in game and each character has a perk that gives you additional XP at level 2 in the first perk slot so I'd recommend using that for awhile once you are able to get it.

Robin has reticent recon which gives you bonus XP for killing players holding a key or chest.
Marianne has Efficient Assassin which gives you bonus XP for assassinations
John has Dying Retaliation which gives you bonus XP for killing players
Tooke has Unwavering Faith which gives you bonus XP for marking enemies.

More XP from:
Marking enemies and players
Assassinating guards and players
Marking objects like rope, portcullis' gear and ammo boxes
Capturing spawn points
Winning a match
Postmatch has 3 awards worth 500XP each for getting the key from the Sheriff, Opening the Vault and getting most notches on the winch.