“前功尽弃”常见的英文表达有：all one's previous efforts are wasted/in vain； lose all one's past gains； throw away all one's previous achievements 。
all one's previous efforts are wasted/in vain：强调之前付出的所有努力都白费了，没有取得预期效果。
例句：If you give up now, all your previous efforts will be wasted.（如果你现在放弃，你之前所有的努力都将白费。）
lose all one's past gains：侧重于失去之前已经获得的东西或成果。
例句：One small mistake could make us lose all our past gains.（一个小错误就可能让我们失去之前所有的成果。）
throw away all one's previous achievements：突出把之前取得的成就都抛弃了，有一种惋惜、懊恼的意味。
例句：Don't throw away all your previous achievements just because of one failure.（不要仅仅因为一次失败就抛弃你之前所有的成就。 ）