Depth of Extinction

The Swashbuckler is not a character class you can pick from the start. Rather, you have to complete the Swashbuckler mini-campaign of a few missions in 3 areas. Once you complete that, you have access to the Swashbuckler. Unlock this achievement by choosing the Swashbuckler option when a recruit is ready to level up for the first time and you have to pick a class for the character and you have completed the mini-campaign.