The 40-year-old, who starred on the field for the Impact in lower leagues before becoming an assistant coach, will replace suspended head coach Marco Schallibaum on the sidelines when the Columbus Crew visit Saputo Stadium on Sunday afternoon.
"Obviously, I'm excited, a bit nervous," Biello said. "You want to win. You want the team to continue to do well."
First-place Montreal (4-1-0) will return to its outdoor home to face the Crew (2-1-2) after playing its first two home games in the domed Olympic Stadium.
The Impact might be wishing they were scheduled to play one more game indoors. Saturday's originally scheduled 2 p.m. ET start time had to be pushed back to noon on Sunday because of snow and rain in Montreal.
The fiery Schallibaum was handed a one-game ban by Major League Soccer when he was ejected from a 2-0 loss in Kansas City two weeks ago for allegedly squirting water at an official.
He will watch from the team's box atop the grandstands as Biello manages the club before a home crowd for the first time. He acted as interim head coach for a two-game exhibition tour of Italy at the end of last season.
"It's important to manage the game," Biello said. "You make the changes, but the bulk of the work is done during the week in preparing the players and how we want to approach the game."
Schallibaum has been running training sessions all week. However, he is not allowed any contact with the team or the coaching staff beginning 90 minutes before kickoff.
The 50-year-old former international defender, who was tossed from games while coaching in the Swiss league before joining the Impact this season, vowed that he never intended to shoot water at the sideline ref after Kansas City scored its second goal.
"I heard the referee came there but it was not my intention to give him the water, I promise you," said Schallibaum, adding that he squirted a little water out of a bottle as a reaction to taunting from the Kansas City bench. It just happened to fall near an official.
"I just maybe made a little provocation also. It was just, not a joke, but it was a little water."
Sporting director Nick De Santis joked that he would "tie him up in a little box with tape over his mouth" to make sure Schallibaum complies with the suspension. But he had no problem with his coach's actions.
"Sometimes emotions get the better of you," said De Santis, a former player and head coach. "Marco's passion transmits itself to the players.
"Do we want him thrown out? No. But things happen. That's what makes him successful — the emotion and energy he brings."
Schallibaum said it's tough for a coach to watch from the stands but he has full confidence in Biello and assistants Philippe Eullaffroy and Youssef Dahha to handle the game.
"The message is the same," said De Santis. "Mauro's been behind the bench before. I don't think it'll make a big difference."
Biello was with the Impact when the club was formed in 1993 to play in the defunct American Professional Soccer League. Although it is only a second year in MLS, the team is celebrating it's 20th anniversary.
The five-foot-nine forward/midfielder was a star playmaker and scorer on the pitch and won three championships in lower leagues. He scored 72 goals in 343 games before retiring as a player in 2009
The Montreal native has since embarked on a coaching career. Some see it as inevitable that he will one day be head coach of the Impact.
"As a coach now, I'm still developing and learning the trade," said Biello. "Eventually, maybe in the future, it could be possibility for me.
"For now, it's about learning and gaining experience and moving on with this part of my career. I've been in soccer for 20 years. I've never done anything else. I wanted to continue in the sport. Coaching has suited me well."
He is of a somewhat calmer disposition than Schallibaum, and is not likely to toss any water on the sidelines.
"I'm going to throw a chair, I think," he joked. "Someone once told me 'When you go crazy, it's got to be big.'"
A slushy field and rainy weather are expected as the Impact look to rebound from their first loss of the season.
They had an unexpected two-week break when a game scheduled for last Saturday in Los Angeles was postponed to October to allow the Galaxy to prepare for a CONCACAF Champions League game.
That allowed time for former Italy international defender Alessandro Nesta to recover from a groin injury. He is expected to rejoin Matteo Ferrari in the central defence.