The plural form of panelist is panelists.

Which is correct panelist or panellist?

As nouns the difference between panelist and panellist

is that panelist is a person who is a member of a panel while panellist is a person who appears on a panel, either as a member of a committee or jury, or as part of a panel game.

Is a panel singular or plural?

The plural form of panel; more than one (kind of) panel.