St. Paul writes of him in an epistle: God grant mercy to the house of Onesiphorus, for he often refreshed me, and was not ashamed of my bonds. When he was at Rome, he searched for me with great diligence, and found me. May the Lord grant him to find the mercy of the Lord on that day; and you know how much he served me at Ephesus. (2 Tim 1:16-18).
He is commemorated by the Church on September 7, and on December 8 with Apostles Sosthenes, Apollos, Caesar, and Cephas and Epaphroditus. The others departed peacefully to the Lord, but St. Onesiphorus died a martyr in the city of Parium (not far from Ephesus) on the shores of the Hellespont, where he had gone to proclaim Christ among the local pagans.
The Apostles of the 70 were chosen and sent by the Lord Jesus Christ himself to preach. They were chosen some time after the selection of the Twelve Apostles (Luke 10:1-24). All seventy are commemorated by the Church on January 4.