Contractors moved in to begin the job last week and when complete the scheme will see the number of spaces at the station increased by 27.
The move follows complaints from the town's community council that the area around the station is frequently congested and that there are more people wishing to make use of it than it can accommodate.
The expansion plans, submitted by First Scot Rail, were well supported and did not attract any objections from neighbours.
As well as creating extra spaces in the main car park, the work will see new lighting added and landscaping of the surrounding area.
It is expected to take eight weeks to complete the project.
Mr Rumbles said: "It is great that the works have now begun to expand the station car park. Obviously there will be some disruption and some spaces will be temporarily unavailable while the works are on-going, but it will be great to have an additional 27 spaces when the works are completed.
"This investment in Stonehaven Station is very welcome, but I will continue to press for further upgrades, including the establishment of a full Stonehaven to Inverurie Crossrail service."