Looking for a very niche definition for a friend, she wants to find a single word that encapsulates the general meaning, "success, but not without hard work" for an article she is writing.
A 'triumph' implies that the success required effort. Similarly a 'conquest' or 'to conquer [a challenge]' may carry this meaning in a nice package. Likewise the idiom "to make headway" isn't one word but carries a meaning akin to succeeding in spite of significant barriers. To 'overcome [something]' may be what you are looking for if there is a specific barrier.
As a verb, you could say surmount or overcome. Both imply achieving victory despite difficulties. But I can't think of noun forms of those words.
You may also use the verb "prevail" in some contexts:
: to gain victory by virtue of strength or superiority : win mastery : triumph — used with over or against (gates of hell shall not prevail against it — Matthew 16:18 (Authorized Version) (the ungodly o'er the just prevailed — Robert Burns)
: to be or become effective or effectual : be successful (the temptation to exploit consumers … usually prevails unless it is curbed — T. W. Arnold)
What about "consummation"?
Although, it's not necessarily as positive "success", it does include hard work and presumably if you were working hard it would be towards a goal you really intended.
Given your friend is writing an article, it could be useful to get some context. However, to me, the verb to master would be a likely candidate:
tr.v. mas·tered, mas·ter·ing, mas·ters \/ General, but careful of lord vs servant connotation \/ 1. To act as or be the master of. \/ if it's a scientific article \/ 2. To make oneself a master of: mastered the language in a year's study. \/ when writing about a personal battle of sorts \/ 3. To overcome or defeat: He finally mastered his addiction to drugs. \/ a rather practical topic, but a tad dated \/ 4. To reduce to subjugation; break or tame (an animal, for example).
He/She [finally] mastered the task/skill...
To achieve mastery in anything implies hard work, time, devotion and so on.
If used in a different context, the results can be silly or oddly laughable, for example:
After I mastered opening a can of beans, I could finally get to cooking.
Now either I'm joking, or I found my nemesis, and it was a can of beans. This sentence, then, really is a bit silly. It's a bit like saying "I showed that can of beans who's boss" or "I totally owned that can". May sound nice in a rap song, not so good in an article...
I think I finally mastered Bach's first of six Cello suites.
Implies that I've achieved my goal (being able to play a piece of Bach). And this also needs no further explanation as to how big a challenge my learning to play this music proved to be. If I were to quantify this, it would make my sentence look (overly?) dramatic, or it would appear that I'm emphasizing how much effort went into this:
I've been playing the cello for the best part of 10 years now, but I think I finally mastered Bach's first of six Cello suites.
Explicitly stating the time just makes me look like a drama-queen, or an insane perfectionist.