If you’re working with a non monospace font, there’s an easy trick to make it monospaced in After Effects (you can also do the same trick in Illustrator).
Instead of using the Horizontal Type tool, use the Vertical Type tool.
Once you’ve added text, add a rotation text animator and set it 90 degrees. This will rotate each character individually.
Next, change the rotation of the actual text layer to -90 degrees.
And just like that you have monospaced text in After Effects!
To solve the problem of spaces (“ “) not being monospaced, you can add the following expression to the source text:
Of course, you can also add monospacing in one click with Type!