The deal will become official upon receipt of his international transfer certificate and a medical test, the team said Thursday. Financial details were not released and Ciman will not have a designated player status.
Ciman, 29, has spent his entire career in the Belgian first division, playing a total of 286 regular season games.
The six-foot central defender is described as a solid tackler and passer who can fill the void left by the departure of Italian Matteo Ferrari. Ciman was also drawn to Montreal to get top-level care for his autistic daughter.
"I'm very excited to join the Montreal Impact and MLS. This will be a new adventure for me and my family," Ciman said. "It is also an opportunity for my daughter so that she could have the proper support and instruction. I would like to thank the president, my agent and all the staff of the club for this new challenge. I can't wait to meet my new teammates, the city and the fans."
Ciman has played nine times for Belgium and was an unused member of the Belgian squad that reached the quarter-finals of the 2014 World Cup in Brazil.
"We are very pleased to acquire a player of Laurent's quality and we are very excited that he has decided to continue his career with our club," said Frank Klopas, the Impact's head coach and director of player personnel. "We were looking for a quality centre back with a lot of experience. He is a key addition to our defence and will be a leader within the group."
Ciman has spent the last six seasons with Standard de Liege and won a Belgian Cup in 2011.
Argentine midfielder Ignacio Piatti is Montreal's lone designated player. The club is still seeking a replacement for departed striker and DP Marco di Vaio.
The Impact open training camp Friday at Olympic Stadium.