A resistor divider will do what you want, but at this voltage there are some issues you can normally ignore:
The top resistor has to be able to handle 1 kV. Those are harder to get than "ordinary" resistors, and are often not linear with voltage at the high end.
Power dissipation. Even what would normally be a "large" resistor, like 1 MΩ, dissipates a whole watt when 1 kV is applied to it.
You need physical distance between two points that have a kV between them for safety and to prevent arcing thru the air.
Due to all these reasons, I would implement the top resistor of the voltage divider with multiple more ordinary resistors in series. For example, 0805 resistors are usually rated for 150 V (your job to check the datasheet). Ten 1 MΩ 0805 resistor in series, physically laid out end to end, can be used as a 1 kV 10 MΩ resistor. The voltage across each resistor will be 100 V or less, which keeps them within spec.
All together, the 10 MΩ string of resistors only dissipates 100 mW, so each individual resistor only 10 mW. No problem here.
With a 10 MΩ top resistor, the bottom resistor of the divider would ideally be 25.06 kΩ to get 2.50 V out with 1000 V in. You want to have a little headroom above the maximum input voltage spec of 1000 V, so a 24 kΩ or even a little lower bottom resistor should do it.
The output impedance of a divider with such a high ratio is basically the bottom resistor value. 24 kΩ may be too high for some A/Ds, so you may want to buffer this with a opamp used as voltage follower.