The Board chose, in an historic vote, to elect Bob Brown.
Here's why:
* "Through" is incorrect: "Through" suggests a method or means of something happening, but the vote itself is the action, not a method.
* "Historic" should be hyphenated: When used as an adjective before a noun, "historic" should be hyphenated.
* Comma usage: A comma is needed after the introductory phrase "in an historic vote" to separate it from the main clause.
You could also phrase it as:
* The Board voted historically to elect Bob Brown.
This option emphasizes the significance of the vote itself, rather than the method used to achieve it.