Yes you can! Enter the Designer and stay on the whole 'Page' (as seen via the navigation bar, just like the screenshot below).
With the whole page selected, on the right hand side of the screen in the Properties Panel, you'll see the 'Font' dropdown, which controls the default font for the whole email design.
Click the 'Edit' option just exactly above the Font menu, and search for the Google Font you'd like to import for use.
(Please visit Google Fonts to preview the available Google Web Fonts.)
If you already know the Google Web Font you want to use, search for it and tick the box beside it, and Save.
Then when you use the Font dropdown menu on any text box like usual, you will see your added Google Fonts in the list of available fonts for use.
To add a Custom Font
Adding a custom font to your design requires an extra step. Once you click the 'Edit' option in the Font menu (as shown previously in the screenshot above), you'll be shown the list of available Google Fonts.
On this screen you should then choose the option at the bottom to add a 'New Font'. Then type in the name of your custom font you wish to add (for example: Gotham, or GothamBold). Then confirm the new font by clicking the tick button, and then the Save button.
The new custom font will now be available to select in the Fonts dropdown menu, but there is one more step to complete the process.
Click on the 'Add your custom CSS' option in the bottom right hand corner of the designer.
This will pop up the Code Editor, and a short piece of CSS needs to be added, in order for the custom font to load and display properly in your designs. See the screenshot below for an example.
Please contact us (at email@example.com) if you would like to set up and use a custom font in your design, and we can help you with the process.