English Translation
He’s resigned his position as chairman of the committee.
Tip: You can also say:
彼は委員会の議長職を辞任した。(i.e. drop the second の and convert 議長の職 into a compound noun 議長職)
彼は委員会議長を辞職した。(pron. いいんかいぎちょうをじしょくした)
彼は委員会の議長職を辞した。(pron. いいんかいのぎちょうしょくをじした)
The original Japanese sentence is not grammatically wrong, but we usually avoid particle の twice in a row. It’s simply because double の sounds unrhythmical. So, I definitely prefer replacing the original sentence with either of the above three alternatives.