The paper presents a new measurement of the electron magnetic moment and the fine structure constant using a one-electron quantum cyclotron. The electron magnetic moment is measured in Bohr magnetons as \( g/2 = 1.001\,159\,652\,180\,73\,(28) \) (0.28 ppt), with uncertainties 2.7 and 15 times smaller than previous measurements in 2006 and 1987. The fine structure constant, \(\alpha^{-1} = 137.035\,999\,084\,(51)\) [0.37 ppb], is determined with an uncertainty 20 times smaller than any independent determination. The electron is used as a magnetometer to accumulate quantum-jump lineshape statistics and its spontaneous emission rate is measured to determine corrections for its interaction with a cylindrical trap cavity. The new measurement and updated QED theory confirm a 1.8 standard deviation shift from the 1987 value and provide a more stringent test of QED, a probe for electron size and substructure, and a search for low-mass dark matter particles.The paper presents a new measurement of the electron magnetic moment and the fine structure constant using a one-electron quantum cyclotron. The electron magnetic moment is measured in Bohr magnetons as \( g/2 = 1.001\,159\,652\,180\,73\,(28) \) (0.28 ppt), with uncertainties 2.7 and 15 times smaller than previous measurements in 2006 and 1987. The fine structure constant, \(\alpha^{-1} = 137.035\,999\,084\,(51)\) [0.37 ppb], is determined with an uncertainty 20 times smaller than any independent determination. The electron is used as a magnetometer to accumulate quantum-jump lineshape statistics and its spontaneous emission rate is measured to determine corrections for its interaction with a cylindrical trap cavity. The new measurement and updated QED theory confirm a 1.8 standard deviation shift from the 1987 value and provide a more stringent test of QED, a probe for electron size and substructure, and a search for low-mass dark matter particles.