The striker claims the prize after she pipped Taylor Hinds and Missy Bo Kearns in a fan poll on Liverpoolfc.com.
The Republic of Ireland international enjoyed a brilliant debut campaign as a Red, scoring 13 goals to help Matt Beard's side clinch the FA Women's Championship title.
Kiernan joined the club in June 2021 to reunite with Beard, who she served under at West Ham United.
At the turn of the year, the 23-year-old put herself in the history books with a six-minute hat-trick in the 6-0 win at Blackburn Rovers – the fastest treble for LFC Women on record.
Her stunning curling effort in that victory was also nominated for FA Women's Championship Goal of the Season.
Kiernan was ever-present in Liverpool's successful league campaign, helping the team put together a 20-game unbeaten run to secure promotion back to the Women's Super League.
Fittingly, Kiernan was on the scoresheet in the Reds' final home game of the season, after which she got her hands on the league trophy.