I also have the same issue. I tried changing the firewall settings, which has worked for other games. I'll probably use some third party thing to play it via LAN or something. But its seriously frustrating.

I tried a direct TCP/IP connection with a few buddies last night trying to host by different people even using the steam mp vs direct connect and it didn't work. I think this i on GBX's end or steam's. Mp in general is just buggy or really bad at the moment. This should be addressed in a patch (I hope) that is coming up in a week or few weeks, time frame is actually unknown so with a grain of salt.

Use log me in Hamachii, I got it up and running in five minutes and didn't have any issues after that.

For anyone else arriving here from Google: Homeworld Remastered still uses the old DirectPlay component for multiplayer. If you're on Windows 10, you have to manually enable this component for multiplayer to work.

To enable DirectPlay, open "Programs and Features" in the Control Panel; then click on "Turn Windows features on or off". In the window that appears, expand the "Legacy Components" item, and check the "DirectPlay" item within the expanded entry. Then click OK.