You can begin preparing for a career as a marine biologist while still in high school. While high school curricula vary by location, Warren Currie, researcher for the University of Guelph, says it's important to get good grades, and to focus on math, science, writing and computer skills.
According to Currie, training to be a top level marine biologist takes up to 15 years. That's broken down as four years to a Bachelor's degree, five or six years in graduate school to become a Ph.D. and four years of postdoctoral school.
Marine biology is a major, but you can also choose to specialize in certain fields such as ichthyology, the study of fish. Not all schools offer such specialized programs, however. If your undergraduate school does not offer marine biology as a major, they may offer biology, microbiology or zoology. These courses can prepare you for graduate study in marine biology.