An analysis of the bottom baryon decay ({\Lambda }{b}\to J/\psi \left(\to {\mu }^{+}{\mu }^{-}\right)\Lambda \left(\to p{\pi }^{-}\right)) is performed to measure the ({\Lambda }{b}) polarization and three angular parameters in data from (pp) collisions at (\sqrt{s}=7) and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The ({\Lambda }_{b}) polarization is measured to be (0.00±0.06\left(\mathrm{stat}\right)±0.06\left(\mathrm{syst}\right)) and the parity-violating asymmetry parameter is determined to be (0.14±0.14\left(\mathrm{stat}\right)±0.10\left(\mathrm{syst}\right)). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.