Do you need Siri turned on to use dictation on a Mac?

No. Dictation and Siri have separate switches, so you can use Dictation with Siri turned off. Apple does not say this in so many words, as explained below. Dictation is turned on or off in Keyboard settings: go to Dictation, then turn it on or off ¹. Apple's steps for turning Siri off do not mention Dictation ².

There is one place where the two meet. Pressing and releasing the Microphone key starts Dictation, but pressing and holding it activates Siri, and only if Siri is enabled ³. If you never hold that key, Siri's setting does not affect Dictation at all.

Why people think Siri is needed

People often link the two because both respond to your voice. Because they are separate features, one can work while the other does not, so Siri answering you does not show that Dictation is working. Test Dictation directly in an app such as Notes or TextEdit before you conclude anything.

Apple's pages do not state outright that Dictation keeps working with Siri turned off. The reading in this answer comes from the separate switches and the steps Apple gives. If Dictation is critical to your work, test it on your own Mac after you change any Siri setting.

Does Hey Siri start Dictation?

No. Saying Hey Siri or Siri is one way to call Siri, and it works only if that option is turned on in Siri settings ⁴. Dictation's three start methods are the Microphone key, the Dictation shortcut and Edit > Start Dictation ⁵, Hey Siri is not one of them, so if Dictation does not start, check those methods and the settings below first.

What to check when Dictation fails

Check these in order, because each one is quick and independent of Siri.

1. Is Dictation on? Open Keyboard settings and confirm the Dictation switch is on ¹.
2. Is the right microphone selected? Keyboard settings include a Microphone source menu for Dictation. On Automatic, the Mac listens to the device it thinks you are most likely to use ⁶. If you use a headset or an external microphone, select it by name while you test.
3. Does it need the internet? Apple says Dictation on a Mac may need an internet connection ⁷. If you are offline and the feature fails, this is the likely reason.

If all three are fine and Dictation still fails, the full list of fixes is in why Mac Dictation is not working.

When Siri has to be on

Siri needs to be turned on before you can use it to get information ⁸. If you want Siri for answers or settings, turn it on in its own pane. That step does not change how Dictation starts, so you can set the two up separately.

If you want the Microphone key to start Dictation only, leave Siri off or accept that holding the key will open Siri. Pressing and releasing it is the Dictation action in either case ³.

The short answer

You do not need Siri on to use Dictation. Turn Dictation on in Keyboard settings and check the microphone and the internet setting if it fails. Siri matters only for requests, for Hey Siri, and for holding the Microphone key. The comparison of the three features is in dictation vs Voice Control vs Siri on a Mac, and the basics of starting Dictation are in how to use Dictation on a Mac.

The terms are defined in the glossary: Siri and Microphone key.