Born near Woodstock, Ontario, Plaskett began the first programs of astrophysical research in Canada at the Dominion Observatory, Ottawa, in 1905. He urged creation of the Dominion Astrophysical Observatory, designed its principal instruments, and became its first director in 1917. With this 1.85 metre telescope, he made observations of stellar motions fundamental to the first measurement of the rotation of our galaxy, demonstrated that interstellar clouds are fairly uniformly distributed through space and discovered the binary nature of the massive star that bears his name. These studies earned him international recognition. He died in Esquimalt.