First of all,Ii am not the creator nor developer of this patch. so for all issues that do occur, I cannot help much with it. That said, it was something posted long time ago by a user of "LymiaAluysia" on the civfanatics forum back in 2017. Link to it here[forums.civfanatics.com]

In the link above it explains how it works, and you just simply install its .exe and your game will be patched with multiplayer.

The overall purpose of this mod is to keep it as simple and painless as possible to load and play mods with people. There are other multiplayer mods and solutions (which i will link at the bottom as alternatives if this doesnt suit you) that are not as easy to work with, but they do exist.

Github[github.com]
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Step one, set your launcher to legacy mode.

• Then, Open up Steam and navigate to your LIBRARY.
  
• Right click on the game in your library and choose "Properties."
  
• Selected the "BETAS" tab.
  
• In the text box to "Enter beta access for to unlock private beta:" enter the password "ineedlegacyaccess".
  
• Click on the "CHECK CODE" button.
  
• You should see a confirmation message that access has been granted.
  
• If not already selected in the drop down, select "legacy" and click close.
  
• Steam may require you to download and update for the game. Wait for this to happen or force it using "LIBRARY -> DOWNLOADS".
  
• Once the game has been updated, click "PLAY" as usual and you will be running the legacy branch.

(copy pasta'd this from the forum thread in the link from previous section, since his instructions are good enough)


Step 2, Download the github file for the mp patch and just run it, it'll ask you to patch/install and from there you'll be all good. that's about it.

Once its patched, quite simply you can just subscribe to any workshop mod, launch your game then goto MODS, select what you want and this time around there will be a Multiplayer option! Have fun with it! ive used this a bunch with other friends and it works well for some mods. It will not however work with any mod that uses .DLLs AND BOTH YOU and the other players must have the same exact mods loaded, so keep that in mind.

• MPMPM[forums.civfanatics.com] & MPMPM Workshop
  
  
• JdH's Civ V Mod Manager (note: this one probably doesnt work anymore? im quite unsure but feel free to test it.)
  
  
• The Manual Method (not so user friendly)