Does God ever answer prayers from non-believers?

Yes.

God hears prayers of non-believers, because a Sovereign receives petitions. A subject has a right to petition, if they are brave enough. What the Sovereign does with a petition, is another issue. It matters how a petition is made.

The clearest example of non-believers making such a petition occurs in Jonah.

Jonah 1:12. Jonah informs the mariners their only hope is to kill him by throwing him overboard. He does not volunteer to commit suicide.

...- And he said unto them, Take me up, and cast me forth into the sea; so shall the sea be calm unto you: for I know that for my sake this great tempest is upon you...

Following this statement, the mariners are more afraid of God, than the storm, until their efforts fail.

vs.13.. Nevertheless the men rowed hard to bring it to the land; but they could not: for the sea wrought, and was tempestuous against them...

This brings us to their prayer in vs.14. God is obligated to hear, but not necessarily grant the following petition.

...Wherefore they cried unto the LORD, and said, We beseech thee, O LORD, we beseech thee, let us not perish for this man's life, and lay not upon us innocent blood: for thou, O LORD, hast done as it pleased thee...

Specifically, they are petitioning God, to be held harmless for an act of murder they have decided to commit. An act, to be clear, they have yet to commit.

Once Jonah was in the water, it was obvious to the men their request was granted. God, in times past, spoke through his prophets. But God's prophet, in this case Jonah, was now dead, and presumably dismembered in a fish. The calm sea state communicated the favorable ruling with no need of a prophet. The takeaway: It matters how a petition is made.

A more complicated example would be the petition made by unclean spirits in Mark ch.5. This however, is more than just a petition. It was partially granted. The takeaway: It matters how a petition is made.

The issue sharpened

I'm answering from the perspective of mainstream Christian theology.

1. The main issue, I think, is how would God apply His own criteria in Prov 15:29 (wicked vs. righteous) and John 9:31 (sinners vs. worshiper & doer of His will) to non-Christians who have not heard the law & the gospel? Those to whom the Bible wasn't revealed yet could have relied on the voice of their conscience and their nature (made in the image and likeness of God), so as Paul said, they are without excuse.

2. So the question is whether there is another criteria God would use for them? Although God would hear everybody's prayers (both righteous and wicked), rather than not responding at all to non-Christian's prayers, God probably will respond positively to the prayers of non-Christians who:

   • tried to obey the voice of their conscience without the law (Rom 1:19-20)
   • worship Him the best they can (Rom 1:21)
   • are not culpable to reject God

   just as how He would respond positively only to the prayers of Israelites and Christians who know AND obey the Law/Gospel AND worship God/Jesus.

3. Another issue is about election. For some denominations, while the elect were still non-Christians God will answer their prayers.

Supporting argument

1. God Himself is on a mission to save the lost, now working through the Holy Spirit knocking on non-Christian's hearts in far fetched place (cf Parable of the lost Sheep, Matt 18:12-14) in concert with Christians who are given the Great Commission (Matt 28:16-20) to bring the gospel to non-Christians (Rom 10:14-15). In his Aug 2022 podcast answer How Are We Born Again? John Piper described how Born Through the Word (our work) works in concert with Born of the Spirit (Holy Spirit's work, who works mysteriously like the wind, John 6:8).

2. Since the Christian God is the creator of all human beings (Gen 1:27) and since He thinks about us (Ps 139:17) and knows every thought (Ps 139:4) I would think He will receive any prayer addressed to creator God even under a distorted (i.e. non-Christian) conception.

3. Some Biblical precedents:

   • Ruth was a Moabite, yet God honored her wish to be included among God's people Israel
   • Naaman was an Aramean (Syrian) military commander worshiping another God, yet the God of Israel healed him through Elisha and accepted his worship afterwards (2 King 5:1-19). Jesus also made his case to be a teaching lesson in Luke 4:27.
   • Jesus responded positively to the plea of a gentile woman living in the region of Tyre and Sidon and praised her for her faith and persistence (Matt 15:21-28).

4. From the credobaptist perspective, every person becomes a Christian through a prayer of repentance while they were still non-Christians.

5. Especially from the Christian Inclusivist perspective, if a non-Christian obeys the voice of their conscience and cries out to God understood through the best concept they know of and in the way that they consider most honorable, then why wouldn't God respond and lead them into the true Christian faith later on?

First, you can rest assured God answers the prayer of an unbeliever or non-Christian when they call upon the name of the Lord in faith. I'm assuming of course that the Holy Spirit has brought the conviction of sin to such a person, as a result of which they repent and seek forgiveness from God.

Second, God is certainly not obligated to answer the prayers of a non-Christian, as John 9:31 and Proverbs 15:29 indicate. Because of His omniscience, however, He obviously hears the prayers of anyone and everyone, whether they are unbelievers, or believers in a "competing" religion, such as Islam.

Third, in the book of the Acts of the Apostles, there is an interesting expression that the author Luke uses to refer to people who are not yet Christians but who obviously believe in God and even have a good reputation among the Jews and the Gentiles. See for example Acts 10:17; 13:43; 17:4 and 17. These God-fearing folks were either converts to Judaism or simply Gentiles who feared God and perhaps even hungered to know God better.

One God-fearing man spoken of in Acts is Cornelius. Though not yet a Christian, Cornelius had prayed to God and was told by a holy angel that his prayers had been answered. Here are Cornelius's words, as recorded in Acts 10:

30 Cornelius said, “Four days ago to this hour, I was praying in my house during the ninth hour; and behold, a man stood before me in shining garments, 31 and he *said, ‘Cornelius, your prayer has been heard and your alms have been remembered before God. 32 Therefore send to Joppa and invite Simon, who is also called Peter, to come to you; he is staying at the house of Simon the tanner by the sea.’ 33 So I sent for you immediately, and you have been kind enough to come. Now then, we are all here present before God to hear all that you have been commanded by the Lord.”

I am reminded of the words of the prophet Jeremiah:

You will seek Me and find Me when you search for Me with all your heart. I will be found by you,’ declares the Lord . . ." (29:13-14).

God hears the heart-seeking prayers of unbelievers. Their hearts, however, must be prepared by God so that they come to realize that Jesus is the One their hearts are seeking.

The apostle Peter, who was called by God to speak to Cornelius, a God-fearer, realized this truth, and he said in the presence of Cornelius and many others who had gathered together to hear Peter,

“I most certainly understand now that God is not one to show partiality, but in every nation the man who fears[or reverences] Him and does what is right [or works righteousness] is welcome to Him.

Peter's words certainly shed light on your question.

In short, since God is gracious, merciful, and omniscient, he hears all prayers, and though not obligated to answer those prayers in the way the one who is praying wants them answered, He does answer the prayers of non-Christians, particularly when those prayers are prayed out of reverence for God.

I once had a professor who disagreed with the old saying that there are no atheists in a foxhole, because according to him, he had known men who refused to believe in God even in such dire circumstances, with bullets flying and bombs exploding all around them. Perhaps my professor was right. Nevertheless, God hears the heart-cry of one who reverences Him and who prays to Him in faith.