The runaway will be played by Gareth Pierce, replacing Bruno Langley who played the role for 16 years.
Langley departed the ITV soap following accusations of sexual assault and later pleaded guilty to groping two women in a Manchester nightclub.
His final scenes aired in December 2017.
Grimshaw will appear back on Coronation Street in the autumn but “the seeds of his return are sown next week (August 19) when a letter arrives in the post”, which starts “months of intrigue and mystery”.
Corrie characters, including Grimshaw’s former partner, the vicar Billy Mayhew, try and track him down.
Welsh-born Pierce’s credits include Stella, Ordinary Lies and Hinterland, as well as Gavin Moss in The Archers.
He said: “I’m thrilled to be joining such an iconic show, and to have been entrusted with taking Todd forward into some really exciting storylines.
“It’s an honour to be part of the dedicated Coronation Street team in such unprecedented times.”
