How do I restrict visibility of custom fields for certain project roles, groups or users?

[Teck-En]

This plugin might helps: https://marketplace.atlassian.com/plugins/com.onresolve.jira.plugin.Behaviours

[Udo Brand]

Note: Behaviours plugin is now included in scriptrunner plugin

[Nic Brough -Adaptavist-]

The other option is the "Field Security" addon from quisapps. The bit I'd like to point out is that "Jira does not do field level security natively - you need coding or an addon to provide it"