Mass-effect – Does multi-player levelling count between games and across platforms in Mass Effect 3

In Mass Effect 3;

• Single Player: Has no affect on your Multiplayer besides you gaining experience with different weapons that would ultimately be harder to get in Multiplayer (i.e. Black Widow, and other weapons of N7 Quality.) Allowing you to know what weapons you want with what mods and classes.

• Multiplayer: - Has a small but noticeable Affect on your Single Player Campaign.

  Whenever you have a successful mission in Multiplayer, you will gain a Galactic Readiness Percentage increase in your Singleplayer (i.e. 5% increase to Galatic Readiness). Every player starts with a minimum Galactic Readiness of 50% (your Galactic Readiness will decay over time if you do not continue to increase it) although there are 6 sectors that make up the "Galactic" Readiness.

  Each sector has a map associated with it in Multiplayer which allows you to increase the Sectors Galactic Readiness by selecting and completing a multiplayer mission on that map. Although if you select random map, in multiplayer, and win you will achieve an increase for all the sectors Galactic Readiness. Another thing to keep in mind is the harder difficulty of Multiplayer mission that you successfully complete (i.e. Bronze, Silver, and Gold) the higher percent of increase to your Galactic Readiness you will receive.

  Your Galactic Readiness affects your war assets in single player completely. Say for example you have 1000 War Assets and only 50% Galactic Readiness, then only 500 of your War Assets will go towards your goal of achieving a victorious ending in single player. Completing a multiplayer mission while having a readiness rating of 100% grants a 5% boost in experience earned.

  Another benefit to single player from multiplayer is the option of adding War Assets to your Single Player Game by Promoting a level 20 character that you have created. This will give you 75 War Assets and this can be done as many times as you wish. This promotion also adds 10 points to your N7 Rating and allows you to start over in Multiplayer on that character.

  Doing harder difficulties in Multiplayer doesn't affect your war assets when you promote your characters. so doing gold in hopes of getting more war assets then doing bronze will only disappoint you.

Some proof for you. Hope this is what your looking for, couldn't find anything else.

Saving the base gives you 110 points towards your Galaxy at War score compared to 100 for destroying it.

There is a rumour that the Illusive Man will be friendlier towards you in ME3 if you went his way in ME2 (saving the base) but that's unsubstantiated.

Since he's (confirmed) trying to kill you in ME3, I don't know how much weight this carries.

The endings below 1750 or above 2800 effective military strength are the same, regardless of what you chose to do in ME2.

The endings, organized by rating required are different depending on what path you chose:

Low EMS Option

Saved the base:

1750-2049 EMS Choose to Save the Reapers and the Earth will be saved.

Destroyed the base:

1750-1899 EMS Choose to become a Reaper and the Earth will be destroyed.

Mid range EMS Option

Saved the base:

2050-2349 EMS Choose to become a Reaper and the Earth will be saved.

Destroyed the base:

1900-2349 EMS Choose to destroy the Repears and the Earth will be devastated

Saved the base only option

2350-2649 EMS Choose to destroy the Reapers and Earth is destroyed.

High EMS Option

Saved the Base:

2650-2799 EMS Choose to destroy the Repears and the Earth will be devastated

Destroyed the Base:

2350 - 2799 EMS Choose to become a Reaper and the Earth will be saved.