The couple first met when Williams, 37, attended an Elevate International retreat 40-year-old Johnson was hosting in Arizona last March.
Johnson, who works with sports teams including the Pittsburgh Steelers, told People magazine, "When we met, both of us were in very similar places on a personal level.
"Michelle was coming off the heels of a really bad relationship, and I was just in a place of despair as well."
The couple say they are planning a short engagement and intend to marry this summer after Johnson proposed to Williams in Pebble Beach, California last month.
Williams, who embarked on a solo music career following a stint in the girl group Destiny's Child, said she introduce Chad to her former bandmates Beyoncé and Kelly Rowland last summer.
Encouraging single people not to worry about being alone, she said: "Don't lose hope in love.
"I do think you should not focus so much that if you're not in love that you get depressed about it.
The 'Say Yes' singer added: "Just don't lose hope.
"But definitely be doing what you can do to make yourself a better person for the person that possibly is on the way for you."
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.