  Uranus' startlingly large obliquity of 98 degrees has yet to admit a
satisfactory explanation. The most widely accepted hypothesis involving a giant
impactor that tipped Uranus onto its side encounters several difficulties with
regards to the Uranus' spin rate and its prograde satellite system. An
obliquity increase that was driven by capture of Uranus into a secular
spin-orbit resonance remains a possible alternative hypothesis that avoids many
of the issues associated with a giant impact. We propose that secular
spin-orbit resonance could have excited Uranus' obliquity to its present day
value if it was driven by the outward migration of an as-yet undetected outer
Solar System body commonly known as Planet Nine. We draw support for our
hypothesis from an analysis of 123 N-body simulations with varying parameters
for Planet Nine and its migration. We find that in multiple instances, a
simulated Planet Nine drives Uranus' obliquity past 98 degrees, with a
significant number falling within 10 percent of this value. We note a
significant caveat to our results in that a much faster than present-day
spin-axis precession rate for Uranus is required in all cases for it to reach
high obliquities. We conclude that while it was in principle possible for
Planet Nine (if it exists) to have been responsible for Uranus' obliquity, the
feasibility of such a result hinges on Uranus' primordial precession rate.
