ambitious can be used to describe both positive and the negative traits of someone's personality, depending on context. Is there some synonym that conveys purely the negative meaning of
ambitious, ie. greed and eagerness to get success, even through unfair means?
Machiavellian springs to mind. Machiavelli's The Prince "is an extended analysis of how to acquire and maintain political power." The "ideal" prince, according to Machiavelli (Niccolò, 1469-1527) is essentially an amoral and ambitious leader of men whose primary and motivating ambition is to acquire, maintain, and extend his power through an end-justifies-means modus operandi.
Offhand, I cannot think of a better "negative" synonym for ambitious.
Careerist (kəˈrɪərɪst) n
- a person who values success in his career above all else and seeks to advance it by any possible means
It's not exactly what you're looking for, but things rarely are.
I think its use is more often negative, more so than "ambitious". It could fit better into a negative context.