Relativistic electrons in the Earth's radiation belts are highly dynamic on a variety of timescales during the geomagnetic storm. Using Van Allen Probe spacecraft data, we investigate rapid enhancements of relativistic electrons in the outer radiation belt during a corotating interaction region (CIR) driven storm. Successive dipolarizations associated with 100keV‐MeV electron injections are identified. The evolution of energetic electrons is analyzed in the space of adiabatic invariants (μ, K and L*). Within less than a few hours, the phase space density (PSD) of the relativistic electrons promptly increases corresponding to injections of MeV electrons. The PSD of MeV electrons cumulatively increases by a factor of 4–10 at L* = 4.5–5.8 which is likely due to successive groups of dipolarizations and injections. Both near‐equatorial (small K) and off‐equatorial (large K) energetic electrons increase significantly. The increases in the near‐equatorial electrons are still dominant, suggesting the operation of betatron acceleration. The event study shows that successive dipolarizations associated with the CIR‐driven storm may rapidly affect relativistic electrons of the outer radiation belt over a wide range in the phase space. Key Points Relativistic electrons increase significantly through a cumulative effect of consecutive dipolarizations associated with a corotating interaction region‐driven storm The phase space density of MeV electrons increases rapidly over a wide range of adiabatic invariants The increase of off‐equatorial electrons is nearly half of that of the near‐equatorial electrons