How to Use Slide Master in PowerPoint (Change Every Slide at Once)

If you've ever pasted the same logo onto 30 slides, or changed the font on each one by hand, Slide Master is for you. It's the template underneath every slide. Change the master and every slide built on it updates at the same time.
Quick reference
| What you want | How |
|---|---|
| Open Slide Master | View → Slide Master |
| Change every slide | Edit the big slide at the top |
| Change one layout | Edit a smaller slide beneath it |
| Go back to normal | Slide Master → Close Master View |
1. Open the Slide Master
Go to View → Slide Master. The left pane changes: the large slide at the top is the master, and the smaller ones beneath it are the layouts (Title Slide, Title and Content, and so on).
2. Change something on every slide
Click the big master slide at the top. Anything you do here flows down to every layout and every slide:
• Add a logo — Insert → Pictures, place it in a corner.
• Change the fonts — click the title placeholder and pick a font, then do the same for the text placeholder. Better still, use Slide Master → Fonts to change the whole theme.
• Change the colours — Slide Master → Colors.
• Change the background — Slide Master → Background Styles.
• Change the fonts — click the title placeholder and pick a font, then do the same for the text placeholder. Better still, use Slide Master → Fonts to change the whole theme.
• Change the colours — Slide Master → Colors.
• Change the background — Slide Master → Background Styles.
3. Change one layout only
Don't want the logo on the title slide? Click the Title Slide layout (the first small one) and tick Hide Background Graphics on the Slide Master tab. Or move and resize the title box just for that layout.
4. Add your own placeholder
On a layout, click Insert Placeholder and choose Picture, Chart, Text or another type. Draw the box where you want it. New slides using that layout will now have an empty box ready in the right spot.
5. Close and check
Click Close Master View. Flick through your slides — the change should be everywhere. If a slide hasn't picked it up, select it and click Home → Reset.
6. Save it as a template
Happy with the design? File → Save As → PowerPoint Template (.potx). Next time, start a new presentation from it and every slide will match from the beginning.
Troubleshooting
My logo appears on some slides but not others. Those slides use a layout with Hide Background Graphics ticked, or someone put the logo on a layout rather than the master.
I can't select the logo on a normal slide. That's the point — it lives on the master. Go to View → Slide Master to move or delete it.
There are lots of masters in the list. Pasting slides from other presentations brings their masters along. Right-click the unused ones and choose Delete Master.
Wrapping up
View → Slide Master, edit the big slide at the top, Close Master View. One change, every slide. Save the result as a template and you'll never line up a logo by hand again.
