The 85-year-old actress, who plays Maw Maw, was credited as a special guest star in the first season.
However, Leachman will be a full cast member when the show returns in the fall, TV Guide reports.
The comedy's creator Greg Garcia also joked that the star will be credited as "introducing Cloris Leachman as Maw Maw".
"I thought it would be funny to make it 'introducing Cloris Leachman' and she thought it was hilarious," he said.
Garcia explained that Leachman could not have been made a regular earlier for scheduling reasons, but said: "I am inspired by her. She's sharp as a tack and here working all hours of the night... She's fun and funny and has great ideas. Her rule is, if it's funny, she'll do it. And she trusts us."
Garcia added that the writers behind the show will be careful about the representation of Maw Maw's dementia, saying: "It's a constant challenge for us. We don't want it to get old and be the same joke... We'll play with it more in season two."
Gregg Binkley, who plays supermarket manager Barney, has already been promoted to a series regular.
Raising Hope, which received an early renewal for season two, will return for new episodes on Fox in the fall. The show continues in the UK on Fridays at 9pm on Sky1.
> Read more TV news