The tree-level amplitudes in the β-deformed supersymmetric gauge theory are derived from twistor string theory. We first show that a simple generalization of [M. Kulaxizi, K. Zoubos, Marginal deformations of N=4 SYM from open/closed twistor strings, Nucl. Phys. B 738 (2006) 317, arxiv:/hep-th/0410122] gives us the desired results for all the tree-level amplitudes up to first order in the deformation parameter β. Then we provide a new proposal which matches field theory to all orders of β. With our deformed twistor string theory, it can be shown that integration over connected instantons and disconnected instantons remain equivalent. The tree-level amplitudes in the non-supersymmetric γ-deformed theory can be obtained using a similar deformation of the twistor string. Finally, we find improved twistor string results for the tree-level purely gluonic amplitudes in theories with more general marginal deformations.