Hagman will reprise his role as J.R. Ewing in the TNT drama when it airs in the summer of 2012.
The actor had to put wife of 57 years Maj into a care facility when he began struggling to look after her himself.
He told the Daily Mailthat being able to work on the series will help keep his mind off his wife's illness and will keep him busy.
"Her Alzheimer's hasn't yet robbed her of the knowledge of who I am," he said. "But I dread that day. It's a cruel disease.
"That's why Dallas is good for me. It made my name the first time around. Now I believe it will save me by keeping me busy and working."
Hagman recently said that it will be "amazing" to return to the soap. An auction of his personal items netted more than $500,000 (£304,971) in June.
> Dallas remake: First look at the return of JR and co