The experienced defender joins United after spells with former Women's Super League sides Bristol City and Reading, and was ranked third-highest in the WSL for shots blocked (19 in total), last campaign.
With over 50 international caps, Gemma will link up with fellow compatriot Hayley Ladd in Manchester – with whom she has formed a formidable centre-back partnership for her country.
Gemma Evans said: “It’s a massive honour to sign here. It’s something I’ve dreamt about. The ambition of the club is what brought me here. Seeing how well the girls did last year was amazing. It’s just an unbelievable feeling to be here now.