Chief executive Brian Caldwell told the club's website: “It is really sad that Stuart feels the time is right to move on.
He added: “He had an exceptional record and generated a huge amount of transfer income for the club.
“He has been crucial to the development of Motherwell academy graduates, as well as the development of young loan players during his tenure.
“When Stuart contacted me, I was very disappointed to hear about the impact this had on his family and how he was feeling. No manager, player or club employee, every one of them giving their all to the club, should feel that way.”
“As a fan-owned, community-driven football club, we will always look after our club,” Caldwell stressed.
The CEO indicated last week that Kettlewell's team was ahead of rivals with bigger budgets and was nine points better at the same stage last season.
However, they lost 2-1 away to bottom club St Johnstone on Saturday, and Well Say Kettlewell approached Caldwell to resign on Monday morning.
The club said: “Stuart explained that some personal abuse had now affected his family, to the point where they did not want to attend matches.”
Kettlewell, who previously coached Ross County in the Championship, has a winning percentage of 41.3% in his 92 matches, which is the highest among his seven managers since the departure of Stuart McCall in 2014.
Well, it must be noted that he led the team to safety from relegation in his first three months in charge, collecting 30 points out of a possible 42, as the team came close to finishing in the top six of the season.
Their 10-match unbeaten run last season was their longest since 2010 as they again narrowly missed out on the top six, while they reached the semi-finals of the Premier League Cup this season.
Assistant coach Stephen Friel will take charge of the team for Sunday's match at home against leaders Celtic.
