Stansted Airport to Cambridge train: usually the fastest public option
Greater Anglia operates direct trains between Stansted Airport and Cambridge. The operator currently lists up to two trains per hour on weekdays and a fastest journey of 29 minutes.
The current route page advertises fares from £9.50 each way, based on a return fare. Ticket prices can vary by time, ticket type and Railcard, so treat that as a live from-price rather than a guaranteed fare for every departure.
On weekdays, Greater Anglia currently lists the first Stansted Airport → Cambridge train at 05:20 and the last at 23:58. Weekend times can differ, so use the live journey planner for your actual travel date.
The big advantage is reliability of journey time: the train avoids motorway traffic and takes you directly to Cambridge railway station.