The 30-year-old from London, Ont., is both Canada's greatest female marathoner and a practising criminal lawyer. And work doesn't stop for the Commonwealth Games where Marchant raced to fourth place in the marathon Sunday.
"I actually picked up a case when I was here, I got an email about an appellate case that another law firm wants me to write for them. Hopefully I'll get the trial transcript Monday," Marchant said, moments after crossing the finish line.
Marchant completed the two-loop course that started and ended at Glasgow Green, a 15th-century park on the bank of the River Clyde, in two hours 31 minutes 14 seconds.
Kenyans finished 1-2. Flomena Daniel crossed in 2:26.45 for gold, and teammate Caroline Kilel was second in 2:27.10. Australia's Jess Trengove won the bronze in 2:30.12.
Australia's Michael Shelley won the men's race in 2:11.15.
Marchant, whose law firm is in Chattanooga, Tenn., is a big believer in balance. She unwinds after a hard run with a beer. And even though her racing schedule has her criss-crossing the globe, she's mastered the ability to combine work and running.
"I just do my work from abroad," said Marchant. "A lot of what I do is appellate cases (court appeals), so I can do the research and write the brief from anywhere in the world. As long as I have an email connection, I can mail it back to them."
Marchant was the only Canadian racing the marathon, which kicked off the track and field competition in Glasgow. She could have passed on Scotland and picked a race with better weather, a better field and better prize money (read: any prize money), but believed that soaking up the experience of her first multi-sport Games was important.
"I want as much experience lining up, with the pressure, wearing the Team Canada bib, being ranked fairly well, so that when I line up hopefully in Rio (2016 Olympics) it's not going to be a shock to the system.
"And at the end of the day, I'm doing this because I want to represent Canada and I want as many opportunities as I can, especially with the times I've not been able to, I'm not going to turn down the chances again."
Marchant, a former steeplechaser at Michigan State and one of seven kids in her family, made a major breakthrough when she broke Sylvia Ruegger's 28-year-old Canadian women's marathon record last year in Toronto, running 2:28.00.
She said life changed for her after that day.
"I'm not used to people really caring what I do in my day to day life and wanting me to blog more. I'm not used to that. And lot of the races I do back in Canada, it seems everybody will recognize me.
"It's a little bit surreal, but I enjoy it and I'm happy to be out there to help garner attention for our sport."
Her mom Mary Lou, a figure skating coach and choreographer, has even shared a bit of her celebrity spotlight.
"She joined the London Pacers, a local masters running group and they're sending the e-mail out about how to join, and were like 'Wait, are you Lanni's mom?' So she feels kind of important which is fun," Marchant said.
She also relishes being a role model, saying a big motivating factor is inspiring young women to run.
"We had a dry spell for a while for long distance running for women in Canada, so I'm trying to show them that if you stick with it, you get out there, you can run," she said. "There are probably a million people out there who could run faster than me."
There were only three on Sunday in a race that was all about placing rather than time. Marchant, her brown hair pulled back in a ponytail under a red cap, ran a tactically smart race that for a while had her within striking distance of a bronze medal.
Namibia's Helalia Johannes was running in third but fading badly. Trengove would pass both and Marchant and Johannes around the 35-kilometre mark for bronze.
"I was trying to (catch third), but just around 37-K my calf started to cramp up on me a little, so I had to make sure and run it smart so I didn't completely cramp up," Marchant said. "So when the Aussie caught me, I kind of figured the medal was out of contention."
"But I wasn't going to give up. And I ended up catching fourth."
The calf cramp wasn't nearly so severe as the debilitating leg cramp that saw her famously stab herself in the leg with a safety pin while running the world championship marathon in 2013 — another runner insisted it would relieve her severe cramp; it didn't.
"It was just bad enough that I couldn't get on my toe," she said of Sunday's leg issue. "So you can't really respond to someone (Trengove) surging past you. But other than that, I was happy with it. I can't really complain."
Marchant ran most of the race alone after a lead pack of eight runners broke apart between 15 and 20 kilometres.
"Lanni had the composure to just lay back and hold on to a rhythm. Played it pretty well," said Canadian distance coach Dave Scott-Thomas. "Lanni's got the temperament and bravery to just go for it, and get the most out of what she's got, and then the intelligence to play it well tactically."
Crowds, in some places a dozen deep, cheered on the athletes, creating a racket by banging on the signage that lined the fences along the route. The runners crossed the River Clyde four times and also negotiated their way through cobbestoned city streets that were made slick by the light rain that fell for much of the morning.
Shelley, meanwhile, improved on the silver medal he won at the Games in New Delhi four years ago, pulling away from the lead group of runners with four kilometres to go.
Stephen Chemlany of Kenya was second in 2:11.58 and Abraham Kiplimo of Uganda earned the bronze in 2:12.23.
"I just decided to stay relaxed on the first lap, not go too hard too early," said Shelley, who buried his face in an Australian flag after his victory. "I don't like the rain too much either, but it's good to come back and defend a silver medal and go one ever better."