There is one difference. The difference between the two is the final result that they are trying to achieve. While proposals are written to win contracts, projects, or work, grants are written to get funding that will be donated to you. This is one of the reasons that when people think about non-profit organizations, they think about grant writing. However, this is not entirely true because non-profit organizations can also win proposals.
The writing process for both grant writing and proposal writing are essentially the same. A smaller non-profit organization or private organization might have one person who will be writing the proposal/grant, while a bigger organization might have a team of people who are all responsible for different pieces of the proposal/grant. One minor difference that could be a major one is that a non-profit organization is usually not run the same as a private organization, which could result in differences in the writing process.
Another difference could be in the actual words used. While they are both written to influence, a proposal will be a bit more technical than a grant should be. A grant should be able to grab you emotionally; a proposal should appeal more to the business side of a person.
What are other differences you’ve seen between grant writing and proposal writing?