Can my warlock benefit both from the Mage Armor spell and leather armor?

Question

Currently making a 5E Warlock for an upcoming session, and I'm wondering how this particular interaction works:

I, as a Warlock, start with leather armor. I'm considering having Armor of Shadows as one of my two Invocations, for at-will self-Mage Armor (DM is starting us off at 3rd level). However, the description of Mage Armor stipulates that "You touch a willing creature who isn’t wearing armor, and a protective magical force surrounds it until the spell ends.", and also that the spell ends if the target dons armor or the spell is dismissed.

So I'm wondering: If I wear leather armor (since I get it starting as a Warlock), can I still use the at-will Mage Armor to have a 13+Dex modifier AC instead of leather armor's 11+Dex modifier AC?

Answer 1

No, sorry.

You can wear leather armor (AC=11+DEX); if you do you cannot cast mage armor on yourself per its description.

Or you can cast mage armor on yourself (AC=13+DEX) and not wear the leather. Naively, this is an unambiguously-superior choice. Two more AC points and, since the invocation gives you mage armor at will, there's no cost in spell slots.

Note, though, that it has cost you: an invocation. That may be a reasonable opportunity cost for your character, but just realize that it's not no cost.

Answer 2

No, the rules for both AC and Mage Armor do not allow it

Player's Handbook, Part 1, Chapter 1, Page 14 says:

Some spells and class features give you a different way to calculate your AC. If you have multiple features that give you different ways to calculate your AC, you choose which one to use.

Theoretically a player can have multiple ACs at one time- but you have to specifically choose which one to use. Additionally, the spell Mage Armor itself doesn't allow you to wear armor (Player's Handbook, Part 3, Chapter 11, Page 256):

You touch a willing creature who isn't wearing armor, and a protective magical force surrounds it until the spell ends [...]

So, even if you wanted to have both leather armor and Mage Armor, you cannot cast the spell on someone wearing armor. Now, Mage Armor could be cast on a monk or barbarian with Unarmored Defense- but you could still only benefit from one AC at a time.