[jones_wise]

Is the focal length of a converging lens always positive - irrespective of whether it forms a real or virtual image?

[Stonebridge]

Yes if you are using the "real is positive" sign convention for the lens formula.
In this, all real object and image distances are positive, and the focal lengths of converging lenses are always positive.
Virtual image and object distances, and the focal lengths of diverging lenses are negative.

[jones_wise]

Thank you!