The station is now accessible from the street to platform with boarding ramps so staff can assist customers who need them.
The lift will also facilitate access for people with heavy luggage or with children in buggies
It joins Wimbledon on the District line and Morden on the Northern line as being a step-free station in Merton.
Martin Whelton, Merton Council cabinet member for Housing, Regeneration, and the Climate Emergency, said: “We welcome these improvements to one of Merton’s busy underground stations that will make travel more accessible. As we recover from COVID making the most of Merton’s outstanding public transport links will be vital in helping our local economy and reducing congestion on our roads.”