User blog comment:Kyz99/How to keep Loyalty/@comment-2256917-20100926060435

The Paragon requirement to stop their fight (and keep loyalty) is about 80% (equals 4 full bars); the Renegade requirement is much lower (about 40%, or 2 full bars). That is, the Renegade option is easier. Before doing the 2nd of their two loyalty missions, if you're in doubt, retrain your powers and take the Class Power Level 4 option that gives an 100% boost to Paragon/Renegade scores. -- Allegedly, if you lose one's loyalty, you can regain it in private conversation later (if you have high Paragon or Renegade points); but it'd better to keep it at the fight.

The key is gaining morality points as you go through the game (see the ME2 Morality Guide if you need details). Choose paragon or renegade conversational choices, always; do Paragon and Renegade interrupts.

Remember: the Renegade option is easier to achieve (to save their loyalty during the fight) than the Paragon option.

If you can't do it, but want to complete the game anyway, then Monkeyfists' option is right. I would put the non-loyal squadmate in Shepard's squad in every part of the Suicide Mission (you can keep them alive), except the last part (since they will die if with Shepard. By the last part I mean of course when you leave the rest of the team to guard the door. Be sure you leave behind tough and loyal defenders, too, like Grunt and Zaeed, to keep your non-loyal members alive).