Marsch made it official after practice on Tuesday, naming the 31-year-old as captain for the expansion team's debut season in Major League Soccer.
The Nederland, Tex. native will wear the captain's armband for the club's first MLS match Saturday against the Whitecaps in Vancouver.
Marsch said that when he was player in MLS he admired and respected Arnaud's battling style.
"Personally Davy and I knew each other a little bit, but I knew him intimately from playing against him," said Marsch. "Frankly, I didn't like playing against him because he was hard to play against."
The MLS version of the Impact, a club that dates to 1993 in lower leagues, started taking shape with the expansion draft on Nov. 18. One player the Impact selected was Seth Sinovic, who was immediately traded back to Sporting Kansas City along with allocation money for Arnaud.
Other veterans were considered for the captaincy, including Brossard, Que., native Patrice Bernier, and Jamaicans Donovan Ricketts and Shavar Thomas, but Arnaud was believed to be the front-runner all along.
Marsch said he liked how Arnaud communicated with teammates on and off the field, and how he led by example with his consistently hard work in training.
Arnaud served as captain the last two seasons in Kansas City, where he scored 43 goals in 240 games over 10 seasons.
"He's been around the league and knows what it takes," said Marsch. "He's a winner and he understands how to help the group move along.
"It's a new responsibility with a new team, but he has people like Patrice and Donovan and Matteo (Ferrari) and Eddie (Sebrango) that will help him lead this team.:
The fact that he is a veteran of the physical, fast-paced MLS game also worked in Arnaud's favour.
"It's important for everyone to understand what these games are going to be like," said Marsch. "That's the reason you see so many MLS guys here.
"It's because I value experience in the league. I value the American player. It's going to be important in what kind of team we will become."
Arnaud was drafted 50th overall in 2002 by Kansas City, then called the Wizards, and established himself as a quick and dangerous offensive midfielder and on-field leader. He also played seven times for the U.S. national team.
In Montreal, he leads that group that has been pieced together over the past six months from many sources, although with a strong contingent with MLS experience.
Arnaud was informed he would be captain after the Impact completed four games at the Disney Pro Soccer Classic pre-season tournament last week in Orlando, Fla. Marsch opted to save the announcement for when the team returned to Montreal for a few days of indoor training ahead of the regular season opener.
"We have a lot of guys in the same boat," said Arnaud. "We've all come from different places, we're all going through the same experiences right now.
"Jesse made that point at the start of camp, that as quickly as possible we jell together, that we have a great attitude and a great work ethic. The front office did a good job of getting guys who are going to have that attitude."
Bernier would have been a popular choice for captain, being a local product who speaks French. He also began his pro career with the Impact in the early 2000s.
But the smooth midfielder is in his first season back in North America after nine years with five clubs in Europe and is still adjusting to the MLS game.
"I know I have a role as a leader on the team," said Bernier. "Being captain is an honour, but it's not something I'm disappointed about.
"Davy is not afraid to say what he thinks. He talks to everybody. He has a good personality. He also works hard on the field. He doesn't just talk. I think that's why he was named captain."
The Impact were admitted as the league's 19th franchise this season. They hope to avoid the struggles most expansion teams have in their first year or two by being competitive right away, although they may not have the depth or the talent on attack of more established clubs.
Marsch wanted to start out with a captain who is a battler, and that was Arnaud.
"He's got a voice within the team and we've tried to encourage that," added Marsch. "It's hard when you bring a new group together.
"There's hesitancy because no one wants to seem like they're the know-it-all. That they're trying too hard. But it's a good group, man. They like each other. They like playing with each other. Those are all good signs. We're seven weeks in (training camp) but it feels like a team and it looks like a team. That's the best part."