This achievement is storyline related!
You must simply recruit any new companion to your cause. I did this with Sera through the Red Jenny quest.
Here are the companions who can net you this achievement:
- Blackwall (Unlock and complete the quest "The Lone Warden" from Leliana on the War Table. He can be found in The Hinterlands)
- Cole (Cannot be missed. Acquired later on in the story)
- Dorian (Fiona will request that the Herald meet with a group of Mages in Redcliffe. Once on this quest, advance it until he forcibly joins your party)
- Iron Bull (Wait at the gate doors outside the Chantry building in Haven. Eventually, a messenger will appear and invite the Herald to The Storm Coast to meet with Iron Bull)
- Sera (When you enter Val Royeaux, an arrow will land near your Inquisitor. Find all the messages left throughout the city)
- Vivienne (In the courtyard of Val Royeaux, there will be a messenger by a fountain near the exit. Pursue the invitation he gives you)