Quick answer
Chromecast with Google TV and the Google TV Streamer run Android TV, so you install TiviMate or IPTV Smarters from Google Play (or sideload with Downloader) and log in. Older Chromecasts without a remote can only play IPTV cast from a phone app.
On this page

Which Chromecast do you have?
| Device | Remote? | How IPTV works |
|---|---|---|
| Google TV Streamer | Yes | Install apps; has an Ethernet port |
| Chromecast with Google TV (4K / HD) | Yes | Install apps from Google Play or sideload |
| Chromecast (3rd gen and older) | No | Cast from a phone app |
Set up IPTV on Google TV
Search Google Play on the TV
From the Google TV home screen, go to Apps → Search for apps and search for TiviMate, IPTV Smarters or XCIPTV. Install your choice.
If the app is not listed, sideload it
Install Downloader from Google Play, then enable it in Settings → System → About → Android TV OS build (click 7 times for developer mode) and Settings → Apps → Security & restrictions → Unknown sources. Then use Downloader as on Firestick.
Log in
Open the app and choose Xtream Codes; enter server URL, username and password.
Tune the playback
In TiviMate set the buffer to large; in Smarters try another player if a channel stutters.

Casting from your phone
On older Chromecasts, open your IPTV app on an Android phone or iPhone, start a channel and tap the cast icon. If your app has no cast button, use an app with casting support, or mirror the screen from Android's quick settings. Keep the phone on the same Wi-Fi and plugged in.
For the full list of players, see best IPTV player apps.
Frequently asked questions
Can I cast IPTV to an old Chromecast (without remote)?
Yes, from a phone app that supports casting — for example IPTV Smarters or a video cast app. Casting depends on the phone and Wi-Fi, so a Google TV model with its own apps is smoother.
What is the best IPTV app for Google TV?
TiviMate for the best guide, IPTV Smarters Pro for simplicity. Both run well on Chromecast with Google TV and the Google TV Streamer.
Why does Chromecast buffer?
Usually Wi-Fi. The Chromecast with Google TV supports an Ethernet adapter/power supply, and the Google TV Streamer has an Ethernet port.