Zander Lehmann is a zero-to-60 peak TV success story.

The creator of Hulu’s “Casual” was working in his first TV staff writing job, on MTV’s “The Shannara Chronicles,” when he sold the script to Lionsgate TV for the offbeat comedy revolving around the romantic misadventures of a brother and sister. In whirlwind fashion, the baby writer had a project on its feet with Jason Reitman, who made “Casual” his first TV pilot directing gig.

“Casual,” a favorite of critics, is just one example of a show that would probably never have seen the light of day but for the voracious demand for original series that has erupted in the past few years, driven largely by streaming services.

On Saturday, Lehmann made the trek to the TV Critics Assn. press tour in Pasadena, Calif., to talk up the third season of “Casual,” which begins shooting Jan. 30 and bows in May. The long odds against his show making it beyond episode three, let alone to season three, are not lost on him.

“It’s really surreal,” Lehmann told Variety. “Three years ago I was 26 and an assistant.”

“Casual” provided him with on-the-job training for becoming a showrunner, a role he splits with fellow exec producers Helen Estabrook and Liz Tigelaar.

Figuring out how to divide up the duties, how to delegate and defer, and generally “who fit in what place” took some time, but the show has found its groove. That was evident from the playful rapport and thoughtful dissection of the characters’ psyches offered on the TCA stage by stars Michaela Watkins, Tommy Dewey, Tara Lynne Barr, and Nyasha Hatendi.

“A year ago I realized I was living in fantasy anyway and now it’s all house money,” Lehmann said of his good fortune with “Casual.” “Now we’re just trying to take wild swings when we can and if it all goes away, I’ve still been here three seasons longer than anybody in my position deserves to get.”

One of those wild swings includes an episode in season three penned by co-stars Watkins and Dewey. “I’m glad they’re getting the chance to put their voices and their names on a script,” he said. “It should be hilarious.”

Another aspect of “Casual” that Lehmann is justifiably proud of is the show’s track record in hiring women directors, including first-time TV helmers. Lehmann, Estabrook and Tigelaar make a list every year of indie films that have impressed them, and they make a push to hire those directors. This year, nine of “Casual’s” 13 segs will be helmed by femmes, including Gillian Robespierre, Amy York Rubin, Lake Bell, and Carrie Brownstein.

“It’s going to give us such a good vision and such a good look,” he said. “The idea of having journeyman directors who are going to get your standard wide shot, your master and move on — that’s not how our show can survive. We have to be visually interesting.”

Lehmann is also starting to spread his wings beyond “Casual.” He has a feature script, “The Beautiful Game,” at Focus Features. And he’s developing an hourlong TV project for Lionsgate with a fellow “Casual” writer. But he has no intention of handing off his firstborn.

“ ‘Casual’ is so much of my voice — it’s hard to imagine really stepping away until the show has finished its run,” he said.