Student or Learner
That he succeeded suprised the panel of judges.
That he succeeded----is a clause acting as the subject of the sentence.
My question is ----what is the function of "that"? As we know , "he succeeded " is also a clause.
I'll give an opinion to start.
"That" is a subordinating conjunction. If the sentence is transformed to:
"(It) surprised the judges that he succeeded." this can be seen immediately. In this case, "it" is the subject of the sentence, but "it" stands for "That he succeeded", so there should be no problem.
Since this is a complex sentence, it has a main clause and a subordinate clause. In the transformed sentence, the main clause is "It surprised the judges" and the subordinate clause is "that he succeeded".
However, in the original sentence, since the main clause must be able to stand alone, the main clause can be taken as the whole sentence, with the subordinate clause "that he succeeded" being embedded in the main clause.