The pair will star in a six-part thriller titled Liar as a couple whose lives are changed forever after one night. Joanne will be changing out of her Ladies Maid attire to take on the role of Laura, a teacher who begins a relationship with the father of one of her pupils, Ioan's character Andrew.
Joanne will star as a teacher named Laura
However, their blossoming romance will have consequences neither of them could expect in the story which examines both sides of the relationship and both sides of the truth.
The show, which has been written by BAFTA and Golden Globe nominated producers and screenwriters Harry and Jack Williams will begin filming in November, and ITV's head of drama, Polly Hill, revealed her delight at the upcoming new series, saying: "I am so delighted to have arrived at ITV and to be working with Jack and Harry Williams on Liar.
"They are brilliant storytellers, who have written a gripping thriller that doesn't shy away from exploring a powerful subject. I'm thrilled we've commissioned Liar for ITV and secured such a terrific cast."
Ioan will play Andrew
The show will be aired in the US on SundanceTV, and the president of the network Joel Stillerman hinted that the thriller is a "page turner."
"Liar is that rare combination of a thoughtful and emotional exploration of the human condition, and a page turner," he said. "The Williams Brothers have created something both relevant and compelling, attributes that the SundanceTV audience respect and embrace."
Joanne is best known for her role as Anna in Downton Abbey
Joanne, who won a Golden Globe for her role as Anna Bates in Downton Abbey, took to Twitter to share the news, retweeting a friend who wrote: "yay for more of my gorgeous pal @JoFroggatt on our screens xx," replying: "thanks angel".