Ms Griffith secured the nomination after incumbent Arfon Jones confirmed he would not be seeking re-election.
Ms Griffith said it was an “honour” to be chosen and described herself as the “continuity candidate”.
Born in Wrexham, Ms Griffith grew up in Barmouth and has lived most of her adult life in Anglesey – serving as the county councillor for the Bro Aberffraw ward until 2017.
She was appointed to the role of deputy in 2016 to assist Arfon Jones shortly after his election and has previously worked as a psychiatric social worker. She also served a public appointment role within the Ministry of Justice.