Johnston previously spent eight years playing for Manchester City and in that time she made over 100 appearances for the club.
During her time in Manchester she enjoyed many successes, which included winning the FA Premier League Northern Division and the FA WSL Continental Cup.
Johnston said: “I’m really happy and excited that I’ve signed for the club. I’m really looking forward to the second half of the season.
“The club’s got a great reputation and I know a lot of people that have played at the club and just by having a conversation with Andy I knew I wanted to come here.
“I was with Georgia Brougham for many years at Man City and I also know Michelle Hinnigan even though I’ve never played with her football-wise.”
Johnston is part of the squad that travelled down to play Watford today at Berkhamsted as the WSL 2 action returns after a month-long break.
“I’ve only met everyone today but it’s been easy to settle into the squad.
“I’m really excited and if I do manage to get onto the pitch hopefully we’ll get all three points.
“I think I bring experience and my pure passion for the game. I’ve got a commitment and a desire to get Everton back where they belong.”
Manager, Andy Spence also believes that the club and Johnston are a great fit as she will be able to make a difference both on and off the pitch.
“We are delighted to have secured the signing of Krystle as she is someone who will bring great experience to the squad.
“After speaking to her I am convinced that we are signing a top person who will really be a positive influence on the players and Club and her quality on the pitch will be invaluable for us.”
Source – everton.fawsl.com