The 22-year-old has signed for the Super League champions on a two-and-a-half year deal to bolster Nick Cushing's attacking options.
Creative, with pace and flair, Lawley hopes to develop her talent and help the Blues to further success.
"I feel to privileged to be here at Manchester City," she told the Club. "I’m excited for the opportunity to show my potential and what I can do.
"The facilities are amazing. I sat down with Nick and spoke about how I can improve as a player – under his leadership and alongside the quality players that are already here.
"I want to become a better player and I hope it will help my international career as well. These facilities and the standard of football will push me on."
Lawley signed for Birmingham in 2013 from Bristol Academy. Born in Kidderminster, she began her career with Arsenal and gained valuable Champions League experience.
The forward has faced her new Club six times for Birmingham, and liked what she saw from the opposition. Now, she is relishing the competition that accompanies joining the reigning double champions.
She recalled: "Playing against City, we always found them hard to break down and they have flair upfront. Hopefully, I can influence and help the club to become even more successful.
"I know a few faces already – Izzy Christiansen played for Birmingham, I’ve played with Nikita Parris for England and I know Abbie McManus from Next Gen – so that’s good.
"I spoke to Izzy at England's senior camp and she obviously spoke very highly of the Club. She told me it would be the best thing I could do.
"I know it’s going to be a challenge to get into the starting XI but it’s a challenge I’m looking forward to. I want to help the team with goals and assists."
Next year brings new tests for City, with the launch of the Spring Series and a tough Champions League quarter-final tie with Fortuna Hjorring - another attraction for Lawley.
She added: "The Champions League is a very high standard and very different to the WSL – it’s more physical with more fitness involved. I'd like to win the Champions League with City."
Manager Cushing was delighted to secure his first signing of the off-season.
"Good, young, English players are what we want to build this team around and we’ve done that consistently," he said.
"Mel is a very good player with real attacking attributes. We know we need to score more goals and we highlighted early on that she could be an asset for us. She was top of our list.
"She has huge potential and we want to build a team the fans can be proud of, who love winning the right way.
"Mel wants to win – she’s ambitious – and she wants to play at the next level, winning some medals. We’re a good team but we want to be better and she definitely gives us that opportunity."