Twin Cities theater leading lady Michelle O’Neill has been tight with megastar Viola Davis ever since they were housemates at Juilliard three decades ago. But O’Neill, who acted in “The Heiress” on Broadway and has commanded stages at the Guthrie, Penumbra and elsewhere, has kept their bond something of a secret, largely to protect the privacy of her Oscar-, Emmy- and two-time-Tony-winning friend.

“We’ve been through all the defining moments of each other’s lives,” O’Neill said. “When she won her first Tony and Oscar. When we got married. When I got cancer and had babies. I remember the whole thing about her bringing [daughter] Genesis into their life.”

The world is getting a peek into the depth of their friendship on “Celebrity IOU,” the newest HGTV show starring Jonathan and Drew Scott of “Property Brothers” fame. The premise of the spinoff is that a star picks a friend whose house could use a makeover. When Davis was approached by the Scott twins for their pilot season, her mind immediately ran to O’Neill, and the Cape Cod in Columbia Heights where the self-described “warrior chicks” had shared much wine and laughter over the years.

“I knew Michelle wanted to renovate her house,” Davis said in a recent three-way phone conversation from her home in Los Angeles. “Family is really important to her. People getting together and connecting is very important to her.”

Built in 1950, the house has charm but had not been updated in decades. Still, O’Neill and her actor-turned-physician husband, Lee Mark Nelson, had made it into a cozy home, one where teenage daughters Ella and Tess had created indelible memories.

“I’m not saying it was a dump, but it was dark and chilly before,” O’Neill said. The thought of renovating it was a far-off dream, both in financial terms, and in her imagination.

“My house was furnished compliments of consignment stores and garage sales,” O’Neill said. As to what Davis and the “Property Brothers” did to the house, it’s something of a marvel, with a new modern kitchen, an open floor plan and even a Zen room. “I don’t think I could have dreamed that big.”

Trusting and letting go

The renovation required trust, which was difficult because O’Neill, by her own admission, has a hard time letting go of the reins. The family loaded up the car last fall to temporarily move to downtown Minneapolis while Davis and the “Property Brothers” got to work.

“When I first drove away from the house, I thought, ‘Omigod, I’ve just relinquished all control,’ ” O’Neill recalled. “It was thrilling because I knew that the outcome was going to be something totally exciting and wonderful, but it was also frightening.”

She did not once drive by to see what was going on.

For Davis, the whole experience was new, and not just the part where she gets to deliver an Oprah-like blessing. (The show paid for the whole renovation.)

Davis found herself smitten with the idea of demolishing things.

“It was all a party for me,” Davis said. “It’s not my house; it’s Michelle’s house, so I was totally into it. I’m like, ‘Knock that wall down. Knock that window down.’ I looked forward to that more than anything else. And here’s the thing, too. By the end, Michelle’s house was going to be a great surprise.”

The friends built their trust by coming through crucibles together. O’Neill, a Boise, Idaho, native who was educated at the University of Utah, first bonded with Rhode Island-raised Davis at Juilliard, where both went for their four-year conservatory training.

They describe that experience as searing, because the school’s rigorous approach to classical actor training required them to be nearly empty vessels. Both were slightly older students with a well-formed sense of self, which meant in-built friction. And they were dealing with younger classmates who were just coming into themselves.

“It was classic sensitive artist stuff,” said Davis. “At Juilliard, whatever your class is, whatever your group, you’re with them for four years, 24/7.”

“24/7,” O’Neill repeated.

“And so we had sort of a shared experience of trauma and misery,” Davis said, busting out laughing.

Another stage

After school, Davis and O’Neill plunged into theater in the nation’s arts capital, New York City. O’Neill landed Broadway roles in a Sam Waterston-led revival of Robert E. Sherwood’s 1938 play “Abe Lincoln in Illinois” (“dismayingly earthbound,” the New York Times said in its pan of the production) and in “The Heiress,” headlined by Cherry Jones. The Times called that production “first-rate.”

The Sept. 11 attacks marked a turning point, geographically, for the two friends. O’Neill and husband Nelson, who married in 1999, decided they wanted to raise a family. They moved to the Twin Cities, where both had acted before and where they had an admirer in Guthrie artistic director Joe Dowling, and bought their home in Columbia Heights.

That same year, 2001, Davis won her first Tony for August Wilson’s “King Hedley II.” Davis, who would win a Tony for “Fences” in 2010, eventually moved to Los Angeles, where she would become an A-list conqueror of TV and Hollywood. She also won an Oscar for “Fences” and an Emmy for playing law professor Annalise Keating in the ABC juggernaut “How to Get Away With Murder.”

The two friends maintained their connection through it all, partly because their shared experiences had created a closeness that made it possible for one to make critical life choices, like a home renovation, for the other.

“We are like sisters that way,” O’Neill said.

As she approached the renovation, Davis had lots of architectural ideas, but they took a back seat to how her choices would fulfill O’Neill’s aesthetic and emotional needs.

“[Michelle] has looked to renovate her house for a while now, especially to combat the Minnesota winters,” Davis said. “So, I said, ‘OK, everything needs to be bright, light, more modern with some traditional elements.’ I think I must have sent her 50 gazillion pictures of kitchens. Then she would send me pictures, and I would say, ‘Well, Michelle, let me tell you why I would like mine better.’ I’m only kidding. But you do sort of know someone’s aesthetic because you know them emotionally — what you feel like they would need.”

Davis treated the renovation as if it were her own home.

“I’m very much into the idea of it being a sanctuary — it’s very Frank Lloyd Wright-ish,” she said. “It should be a shelter, a place of peace and all of that. I felt … everything should have a very open atmosphere, so that when people get together, they’re in one space.”

The two friends also share a fondness for warmth.

“And fireplaces — I love fireplaces,” Davis said.

HGTV has been running teasers of the episode, which airs April 27, showing O’Neill squealing with joy at the reveal.

“This is such a gift, from Vi and from Jonathan and Drew, who I could not thank enough,” O’Neill said.

As they wrapped up their phone conversation, the two friends flashed back to their respective reactions when they first heard about the “Celebrity IOU” idea. Davis recalled how the “Property Brothers” approached her at the Emmys “three or four years ago.”

“And they said, ‘Viola, you know, we’re gonna be doing this show with celebrities; you pick a friend, and we renovate their house,’ ” Davis said. “And I was like, ‘Really?’ And he said, ‘Yeah, we’d love for you to be a part of it.’ And I said, ‘Don’t promise that and not follow through.’ And that’s how it started, with them kneeling at my feet at the Kodak Theatre.”

Excited, Davis tried to reach O’Neill to gauge her reaction to the idea, but her friend was on a flight from seeing family in Boise.

“I got off the airplane, and there were like eight texts from Vi — ‘Call me, call me, you’re gonna love me more than your mother!’ ”

“That’s my big thing — I say that too much,” Davis said.

Years went by until everything came together in a rush last fall.

After the renovation was complete and the big reveal, they all had a post-show party with Davis, her husband, Julius Tennon, and their daughter, Genesis; O’Neill’s husband and daughters, plus Jan O’Neill, her mother; and friends including Dowling and actors Steven Yoakam and Sally Wingert.

O’Neill’s trust in her friend was validated.

“It was a dream I couldn’t imagine but now I can, because I’m living in it,” she said.