The building in Carluke, South Lanarkshire, is the base of Clydesdale MSP Aileen Campbell.
Vandals smashed a window and spray-painted ‘SNP out’ on the front of the office in the town’s Kirkton Street.
Officers were in attendance at the scene this morning.
One passerby told The Scotsman: “The staff are in shock. It’s a horrible thing to have done.”
Carluke lies within a key marginal seat being defended by the SNP’s Angela Crawley at next month’s general election.
In a statement, Ms Campbell said the incident had left her “saddened”.
She added: “I have a duty of care for the people who work in my office and this is clearly upsetting for them.
“People can disagree about politics, but there is no excuse for mindless aggression, vandalism or violence which causes stress and anxiety in local communities.
“We should strive for a better politics that respects and seeks to understand other points of view, and thankfully, that is how most people conduct themselves.
“We won’t be dragged down by the mindless act of a minority.
“We’ll clean this up and my service to my constituents will not be affected.”
Reacting to the news, local SNP candidate Ms Crawley said: “It was incredibly disheartening to learn this morning that my colleague’s parliamentary office has been targeted in a hateful act of vandalism. Truly sorry that her staff had to arrive to work to see this mindless demonstration on a publically funded office.”
A police spokeswoman said the incident was believed to have taken place between 9pm on November 26 and 8am on November 27.
Anyone with information is urged to call police on 101, quoting incident number 0634 as of today.