Lumsden, who arrives at the club from Portsmouth Women, progressed through the ranks at Arsenal Women and has experience playing for Chelsea Women, Millwall Lionesses, Charlton Women and Southampton Women in the past.
The attacker arrives with much goalscoring pedigree, netting 27 times in 33 appearances for Oxford Women in 2021/22, and moves to Newcastle after helping Portsmouth top the FA Women's National League Southern Premier Division - the southern equivalent of the Magpies' current league.
The addition of Lumsden is a further indicator of the ambition of Newcastle boss Becky Langley, as United strive to get promoted from the third tier at the first time of asking.
"Beth is an exciting player who has proven herself in the Championship," said Langley. "She's got quality with both feet and will score goals, no doubt.
"I've worked with Beth before so I know what she's about and she has a good competitive edge to her game. We are excited she's on board at Newcastle."
Upon signing, Lumsden said: "I'm super excited to be here and can't wait to get started.
"It's a very exciting time to be a part of this team, with the ambition of the club matching my personal ambitions. I knew it was the right move for me."
Lumsden will be available for selection when the Magpies host Nottingham Forest Women at Kingston Park on Sunday. Get your tickets here.