A graduate of the Shillong Lajong FC Academy, Lachenpa signed a professional contract with the Meghalaya-based club in 2015. The Sikkemese shot-stopper made 24 appearances during his four seasons there, before signing for fellow I-League club Real Kashmir in 2019.
"It's a proud moment for me, taking the next step of my career and committing my future to a club of Mumbai City's stature. I've enjoyed my football and my journey so far but I'm only getting started," Lachenpa said in a statement.
"I know I have to work harder and I am really looking forward to working with and learning from my teammates. It's a huge challenge and an even bigger opportunity for me and I am ready to give it my all," he added.
A regular starter in Real Kashmir's fourth-placed finish last season in the I-League, Lachenpa impressed as he kept 8 clean sheets in 19 appearances across all competitions, conceding only 17 goals in the process. The youngster will join goalkeeper Amrinder Singh in the goalkeeping contingent at Mumbai City.
Head coach Sergio Lobera said, "Phurba was one of, if not the best goalkeeper in the I-League last season, and we are delighted to have him here at Mumbai City. He is young and has tremendous potential to improve a lot in the future. Phurba's reflexes and command during the games is something that caught our eye, and we are hoping he can continue his development here at Mumbai City, and play a huge role in the club's successes for years to come."