Seriously? 'long career' can't be translated as 'carrière longue'?
No, really I would not use "long" to translate "belle" in this sentence: a "great" career?
Right: the original version is the English 'long', so the translation should be 'longue'. Of course a 'long career' can be intended to mean a 'great' one too, but that's not a direct translation.