The theory of Markovian processes is used to investigate the bivariate distribution of chain length and composition in free-radical polymerization consisting of N types of monomer. By following the matrix calculation procedure, it is straightforward to determine the full composition distribution of polymers with a given chain length numerically, with the help of computer softwares capable of conducting symbolic calculations. For long polymer chains, the instantaneous composition distribution is approximated by a Gaussian distribution and the variance is inversely proportional to the chain length. These features are the same as those for copolymers (N = 2), which is conveniently represented by the Stockmayer bivariate distribution. Simpler numerical methods to determine the variance of the composition distribution are proposed. The Gaussian approximation of the composition distribution is a practical method to theoretically calculate the bivariate distribution formed in multicomponent polymerizations.