Essex Police stated Wednesday that they had detained 36-year-old Gavin Plumb "as part of an ongoing investigation."
Additionally, he has been charged with inciting others to commit kidnapping.
On Thursday's episode of This Morning on ITV, Willoughby was absent. On Thursday night, she was reportedly under police protection in her own house.
It was reported in The Sun that Willoughby was the intended victim of the scheme, however Essex police have not confirmed this.
The publication reported that digital devices and a mobile phone were seized by police after the arrest and that they contained "sinister messages" threatening to abduct and "seriously harm" the celebrity.
In a statement, Detective Superintendent Rob Kirby said: "This was an extremely fast paced investigation, with many of our officers and national partners working overnight to secure these charges."
"The safeguarding of any victim is paramount and we will continue to prioritise this and working with the Metropolitan Police Service as the investigation proceeds."
Willoughby, 42, has hosted This Morning since 2009, nevertheless has had a rough few months leading up to this incident.
An online uproar began a year ago when the broadcaster was accused of "jumping" the queue to see the Queen's lying-in-state.
Willoughby and her then-co-host Philip Schofield refuted the allegations, stating they were actually filming a special report at Westminster Hall.
Schofield resigned in May after reports of deteriorating tensions between the two parties.
He lied to his coworkers about his affair with a much younger colleague, but subsequently acknowledged having one.
During the aftermath, Willoughby indicated she would continue as a presenter but took time away from the show to let the dust settle.
She said she was "shaken, troubled, and let down" by the events in an on-air statement after her return.
Then, this summer, a "large number" of ITV staff, both present and past, reportedly wrote members of parliament to complain about "toxic working cultures, bullying, discrimination, and harassment" on ITV daytime shows like This Morning.
The BBC tried to get Willoughby's publicist and agent to talk about the alleged kidnapping plot, but they both declined and said they should go to the police instead.
