The talented forward has scored 19 times in 47 games for the famous English club since her debut in 2021.
Her debut season saw her find the back of the net 14 times in 2021; however, the following season was marred by a serious injury in the 2022/2023 season.
Last year, Kiernan returned to the side and scored four goals in a campaign that saw them finish fourth.
The 25-year-old has also played 32 times for the Republic of Ireland, scoring four goals in that period.
Speaking on the club's website, Kiernan expressed her fondness for Liverpool and acknowledged the relationship between the city and Ireland.
"I love the club, I love the fans, I love the people. We are very similar, the Irish and the Scousers, and I really feel at home here.
"It is massive for my family as well. Obviously, they come over quite often, which is really nice, and it is the closest city to Dublin. They really enjoy coming over, and when I told them I was getting a new contract, they were ecstatic."
Liverpool's final pre-season friendly is against Everton at St Helens Stadium this Sunday, before they host Leicester City to kick off the 2024-25 WSL campaign a week later.
