The normalized differential cross section for top quark pair ( ${\mathrm{t}}\overline{{\mathrm{t}}}$ ) production is measured in pp collisions at a centre-of-mass energy of 8 $,\text {TeV}$ at the CERN LHC using the CMS detector in data corresponding to an integrated luminosity of 19.7 $,\text {fb}^{-1}$ . The measurements are performed in the lepton $+$ jets ( $\mathrm {e}/\mu $ $+$ jets) and in the dilepton ( $\mathrm {e}^+\mathrm {e}^-$ , $\mu ^+ \mu ^- $ , and $\mathrm {e}^\pm \mu ^{\mp }$ ) decay channels. The ${\mathrm{t}}\overline{{\mathrm{t}}}$ cross section is measured as a function of the kinematic properties of the charged leptons, the jets associated to b quarks, the top quarks, and the ${\mathrm{t}}\overline{{\mathrm{t}}}$ system. The data are compared with several predictions from perturbative quantum chromodynamic up to approximate next-to-next-to-leading-order precision. No significant deviations are observed relative to the standard model predictions.