1 what new testament book was written first

The New Testament book that was written first is generally considered to be 1 Thessalonians, which was written by Paul the Apostle around 50-51 AD.

Paul wrote 1 Thessalonians to the early Christian church in Thessalonica, Greece, which he had founded during his second missionary journey (Acts 17:1-9). The letter is a response to questions and concerns that the Thessalonian Christians had about the second coming of Jesus Christ and the end times.

The earliest manuscripts of 1 Thessalonians date back to around 200-300 AD, but most scholars believe that the letter was written earlier, likely within a decade or two of Paul's death in 64-67 AD.

Other early New Testament books include:

It's worth noting that the exact order and timing of the writing of the New Testament books is still a matter of scholarly debate and ongoing research.