Paul names himself as the writer
The opening line gives the clearest answer. Paul identifies himself as an apostle of Jesus Christ, writing to God's church at Corinth, and he includes Timothy as a brother with him (2 Corinthians 1:1). So, 2 Corinthians is a letter from Paul.
Paul did not claim his role as an apostle because he had earned it. He says it came through God's will. That matters because the letter is not simply one person's advice to a troubled church. Paul writes as Christ's sent messenger, with a deep responsibility to care for believers in Corinth.
Paul, an apostle of Jesus Christ by the will of God, and Timothy our brother, unto the church of God which is at Corinth, with all the saints which are in all Achaia:
What about Timothy?
Timothy is named in the greeting, but this does not mean Timothy was the main author. In the ancient world, trusted co-workers were often included at the start of a letter. Timothy had served alongside Paul and was known to the Corinthian believers.
As the letter continues, the writer repeatedly speaks of his own experiences, decisions, prayers, suffering, and ministry. Paul recalls his concern for Corinth and explains that his actions toward them were shaped by love, not by a desire to control them (2 Corinthians 1:23-24). Timothy was a valued companion, while Paul was the letter's author.
A very personal letter
2 Corinthians is one of Paul's most open-hearted letters. He tells the church that he and his companions had faced crushing trouble in Asia and had learned to rely on God, who raises the dead (2 Corinthians 1:8-9). He also describes arriving in Macedonia with outward conflict and inward fears, before God brought comfort through Titus (2 Corinthians 7:5-6).
These details give the letter its personal feel. Paul was not writing from a distance as a detached teacher. He knew hardship, disappointment, reconciliation, and comfort. He wanted the Corinthians to see that Christian ministry can look weak on the surface, yet still be sustained by God.
For we would not, brethren, have you ignorant of our trouble which came to us in Asia, that we were pressed out of measure, above strength, insomuch that we despaired even of life: But we had the sentence of death in ourselves, that we should not trust in ourselves, but in God which raiseth the dead:
Why Paul's authorship matters
Some people in Corinth questioned Paul's authority and compared him unfavourably with more impressive voices. Paul answers without pretending he is strong in himself. He describes a continuing weakness that drove him to seek the Lord, then points to Christ's grace as sufficient and Christ's power as most clearly displayed in weakness (2 Corinthians 12:7-9).
That is a key to reading 2 Corinthians. Paul wrote it, but its centre is not Paul. Its centre is the God who comforts the afflicted, reconciles people through Christ, and works through ordinary, fragile servants. Reading the whole letter will let you hear both Paul's honesty and his steady confidence in Jesus.
And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.