Short answer
You can sell it, but the occupant is a problem the buyer will price in. You cannot remove someone yourself by changing locks or shutting off utilities. Philadelphia Municipal Court says it cannot hear a squatter case, so a different court process applies. Talk to a Pennsylvania real estate attorney before you act.
Why this is tricky
When a person lives in a house without a lease, the legal category matters. Are they a former tenant, a relative, a guest, a person who was told they could stay, or someone with no permission at all? The label changes the steps. A tenant without a written lease may still have rights.
The Philadelphia Municipal Court pamphlet says that court hears cases about written or oral leases but cannot hear a case involving a squatter. It also says self-help by a landlord is not permitted. So you cannot solve it by locking someone out.
If the occupant is a family member or former tenant, the facts may be more ordinary than they feel, and a conversation or a written move-out agreement can resolve it. Start there when it is safe.
What you can do
Start by documenting the facts. Who is there, since when, and under what agreement, if any. Gather proof of ownership and any messages about the arrangement. Then speak with a Pennsylvania real estate or landlord-tenant attorney about the right proceeding. This answer does not describe the correct court process for a true squatter, because the sources we reviewed did not.
Police may or may not get involved depending on facts. An attorney can say what to expect.
Keep your own safety first. If you feel threatened, call the police and let an attorney sort out the property side later.
Selling while the occupant is there
Some buyers will buy as-is with the occupant in place and handle removal themselves. They will price in time, legal fees and risk, so the offer will be lower. A buyer using a mortgage is unlikely to proceed.
Pennsylvania's Seller Disclosure Law applies to sales of one-to-four-unit homes, and asks about legal issues affecting title or use of the property. Be honest on the form about the occupancy.
Agreement with the occupant
If the occupant is willing to leave, a written agreement with a move-out date, and possibly a payment, can be faster than a court case. Put every term in writing and have an attorney review it. Do not threaten, and do not offer anything you are not ready to pay.
A buyer will probably ask for a written statement from you about the occupancy history, and that statement should match what you put on the disclosure form.
Where a cash sale fits
Kaizen Home Buyers buys as-is, makes a cash offer within 24 hours and charges no agent commission. Whether we can take a house with an unauthorized occupant depends on the facts, so call 267-329-0084 and describe the situation honestly. If you can resolve the occupancy first, a listing with an agent may bring a higher price.