how to make a custom field required

[Joe Pitt]

If you want it required on creation put it on the create screen and mark it as required in the field configuration scheme used for the project. If you want it required on a transition install jira-suite-utilities, which will allow you to mark it required in a transition. Don't forget to put it on the transition screen.

[Paulo Hennig]

Hey Jen,
You can use the following guide for that:

• https://confluence.atlassian.com/display/JIRA/Specifying+Field+Behavior#SpecifyingFieldBehavior-Makingafieldrequiredoroptional

Basically you just need to make required in the Field Configuration for the issue type/project.