The former Destiny's Child singer revealed the news in an Instagram story post which is no longer available.
The 38-year-old singer wrote on the day she released her new single Fearless: "I still remain fearless. I guess I still remain single! Things didn't work out. The healing that needs to take place is a must!"
"I don't wanna destroy another relationship. Blessings to him, his family and ministry. #FEARLESS."
The former couple first met when Williams, 37, attended an Elevate International retreat which 40-year-old Johnson was hosting in Arizona.
They later starred in a reality show called Chad Loves Michelle sharing their pre-marriage journey with viewers.
Williams told reporters while promoting the Oprah Winfrey Network show that counselling had helped them connect better as a couple.
She explained: "I had to learn how to communicate all over again. I've been on my own over 20 years - you don't have to tell me what to do.
"This is my house; you know? And, it's like - now all those things are going to change. How do you communicate that? How do you communicate your fears and concerns in those areas?"
In an interview with People magazine, Williams admitted that she fell into a deep depression as she began planning her summer wedding.
She said she secretly broke off the engagement just weeks after Johnson had proposed and again a few months later - just hours before she checked into a treatment facility for her depression.
The star posted a picture on Instagram with the caption: "Depression sucks, but my faith in God and my commitment to doing the work to stay well is my way out!"
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