Most recently, however, Tupper has transitioned from covering up crimes to solving them, with his latest role as an FBI agent working with an archaeologist (Courtney Thorne-Smith) to solve a murder in Hallmark Movies & Mysteries' Site Unseen: An Emma Fielding Mystery.
"I think Hallmark is doing this really exciting thing right now, where they buy a series of books, they're books for young adults, or adolescents, and they're really fun Agatha Christie-style mysteries," the Canadian actor excitedly told ET over the phone earlier this month. "I actually signed on for three of them."
Though Site Unseen has yet to premiere, Tupper said he hopes to work on the next Emma Fielding installment, should Hallmark officially order more. (Nothing has been confirmed at this time.)
"The plan is to go ahead and make them if it’s successful, so I'm thrilled," he said of the six novels by Dana Cameron. "They want to create a kind of fun, sustained relationship. So I thought the project really hinged on me and Courtney Thorne-Smith, the fun that we could have together and what we could make of it, and she's just amazing. It worked in a really nice way."
"It was one of the funnest projects I ever did, I'm not going to lie," he continued. "[Thorne-Smith and I] both realized that the heart of the project was in our relationship. It's fun to solve a mystery, but it's even more fun to watch two people kind of dance around a relationship and be playful with each other."
The confluence of archeology and crime solving isn't a new topic for Tupper, whose longtime partner, Anne Heche, starred in USA's 2015 miniseries Dig -- though the actor laughed that he and Heche could have compared notes if they’d recognized the connection sooner.
Tupper and Heche's careers have overlapped several times throughout their decade-long relationship. The two met while starring as love interests on 2007's Men in Trees, and played a married couple in 2016's Syfy series Aftermath.
"We do [discuss our work] when it's a comedy. When it's a mystery like this, or a thriller like this, it would be fun. When you're chasing creatures from the middle earth and there's blood on your face, we tend to try to leave it behind," he explained, telling a story about how Heche once ordered him and his "grizzled" Revenge character, David Clarke, out of their home during the show's "dark" fourth season.
Heche was much more excited about Tupper's role on Big Little Lies, however.
"She's been in the limelight for a long time, she's had an amazing career, so I think she was thrilled for me to finally be on something that was really, probably going to get recognized."
Big Little Lies definitely made a big impact, earning awards buzz even before it premiered on HBO in February. "I had a feeling [it was going to be successful] when I watched the Golden Globes a month before Big Little Lies premiered," Tupper shared. "Nicole Kidman and Reese Witherspoon were giving the award for Best Limited Series, and I was like, 'Are they not teeing that up for next year?'"
From day one, Tupper said everyone brought their A-game. "It was pretty serious [on set]. The most serious was actually [Alexander] Skarsgard. I'd be like, 'Hello!' and he'd just sort of nod his head at me, like a sinister force. There wasn't a lot [of joking around], because it's a bunch of pros and everybody's working," Tupper recalled.
Though the violence Skarsgard performed with his on-screen wife, Kidman, understandably put him in a different headspace, Tupper's role wasn't without its own challenges.
"[Punching Adam Scott] was one of the hardest things I ever had to film, because I like him so much," he joked, adding that the two became such good friends that the actor stayed for weeks in his "cabin in the woods." "We had so much fun working together and, you know, you try to kind of hold the relationship, because there's not a ton of rehearsal time. You just run and shoot it, you know. So you're kind of trying to have that relationship with him, and he was such a hard guy to dislike."
Witherspoon, too, provided Tupper with a few laughs. "The funniest thing that happened to me was the first day I walked on set, Reese was in her makeup chair, and I walked in, and she's like, 'I hope you don't think Nathan's not responsible for losing out on the opportunity of raising his daughter.' I'm like, 'Well, someone made it untenable.' She was like, 'What?!'" he remembered, chuckling over the rise he got out of the Oscar winner. "We started right off. She's great. I gotta tell you, being in that group of artists... everybody has some really special skills and you kind of get on set and you wait to see it."
A second season was initially shut down by director Jean-Marc Vallee, but has since been teased by author Liane Moriarty and Witherspoon. Tupper said that more episodes would be "fantastic," given that it was pretty much his idea to begin with.
"I told [Witherspoon] when I was there, I said, 'What you should do is you should buy another Liane Moriarty novel, because she's a terrific storyteller, and then put a lot of the same cast into it.' Like, a star cast, get Vince Vaughn in there or something, Colin Farrell, and then do the next novel. Then I read a few weeks later that she bought the next novel, so I don't know if she's going to do it or not," he said. "But I'd love it. I'd love to do another series."
"That's definitely above my pay grade," he cracks when asked if he has any idea of where the series could go with another season. "But I pitched that I would become a superhero, with a cape and stuff, driving like, an old, 1970s gold Corvette!"
Site Unseen: An Emma Fielding Mystery airs Sunday, June 4 at 9 p.m. ET/PT on Hallmark Movies & Mysteries.