It is thought that much of the mRNA processing occurs co-transcriptionally. However, it remains debatable when it exactly happens relative to transcription. Here, we leverage the Nanopore direct RNA sequencing to interrogate the timing of splicing and m6A deposition during transcription in mammalian cells. We find that most of the splicing catalysis occurs after the transcription termination and cleavage. We also find that much of m6As is already deposited to unspliced nascent mRNAs. Interestingly, these m6A marks are depleted around exon junctions, suggesting that at least part of the selection of m6A deposition occurs before splicing. These observations revise the current understanding and suggest m6A deposition, transcription termination, and splicing to occur in this order in mammalian cells.