Was Paul married? I believe to be a member of the Sanhedrin he was, but I understand the Bible does not indicate this.
I know of no reference that indicates a member of the Sanhedrin had to be married. Just to be sure, I checked numerous references, including Jewish Encyclopedias, and found no such requirement. Membership on the Sanhedrin was mostly a political appointment where scholarship was considered as a secondary factor. I see numerous claims that it was a requirement, but none indicate sources, which tells me this is probably an urban legend.
"According to R. Jose b. Halafta, the members of the Great Bet Din were required to possess the following qualifications: scholarship, modesty, and popularity among their fellow men (Tosef., Hag. ii. 9; Sanh. 88b). According to an interpretation in Sifre, Num. 92 (ed. Friedmann, p. 25b), they had also to be strong and courageous. Only such were eligible, moreover, as had filled three offices of gradually increasing dignity, namely, those of local judge, and member successively of two magistracies at Jerusalem (Jose b. Halafta, l.c.). R. Johanan, a Palestinian amora of the third century, enumerates the qualifications of the members of the Sanhedrin as follows: they must be tall, of imposing appearance, and of advanced age; and they must be learned and must understand foreign languages as well as some of the arts of the necromancer (Sanh. 19a)." [Jewish Encyclopedia, "Sanhedrin."]
What I suspect has happened is that there were regulations for non-Israelites' placement on the Sanhedrin. A proselyte could be a member, only if he married an Israelite woman. This rule had nothing to do with whether full Israelites could be seated in the Sanhedrin if they were single.
Paul stated that he was not married. Because of the approaching persecution (I Corinthians 7:26), Paul urged Christians to refrain from marriage as he had done, if they could. "But I say to the unmarried and to the widows: It is good for them if they remain even as I am" (I Corinthians 7:8). In defending his apostleship, Paul stated that the fact the didn't have a wife with him didn't make him less of an apostle. "Do we have no right to take along a believing wife, as do also the other apostles, the brothers of the Lord, and Cephas?" (I Corinthians 9:5).
Not that it mattered because Paul wasn't a member of the Sanhedrin. There are indications that he was being groomed for the position. "And I advanced in Judaism beyond many of my contemporaries in my own nation, being more exceedingly zealous for the traditions of my fathers" (Galatians 1:14). But it is fairly clear that Paul wasn't actually a member.