The first comprehensive biography of Euler in English is Ronald Calinger's Leonhard Euler: Mathematical Genius in the Enlightenment, available from Princeton University Press. For a list of other biographical resources, see our resources page.
Additionally, the Euler Archive is fortunate to have available two lengthy eulogies of Euler published shortly after his death. Both were published originally in French, and both have been translated by John S. D. Glaus of the Euler Society. Glaus has kindly allowed the Euler Archive to publish his translations here.