(This is a follow up question to my question about combining GPLv3, Ms-PL and BSD licenses).
I have a piece of software I would like to release under the GPLv3, however it requires two other pieces of code - one which is Ms-PL (Microsoft Public License) licensed and one that is BSD licensed.
Is it possible to distribute the code under three licenses, that is to keep the original licenses of the Ms-PL and BSD licensed code parts as is, and just license my code under GPLv3?
You could do that, but it will be very fishy. If you wrote all the GPL-ed code yourself, then the best way to do this would be to add an exception clause, like
YourProduct is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. As a special exception, the copyright holder grants your permission to link the product with package A and package B, [...]
If you didn't write all the GPL-ed code yourself, you can't do that, because you don't have the right to relicense the code written by others.
In any case, you may want to contact the Free Software Foundation or a similar group so they can offer advice on the situation and perhaps suggest a more airtight wording if you want to go with an exception clause.