If a person dies following a religion other than Islam, then Paradise will be forbidden for him, because Allaah says (interpretation of the meaning):
“Verily, whosoever sets up partners (in worship) with Allâh, then Allâh has forbidden Paradise to him, and the Fire will be his abode” [al-Maa’idah 5:72]
Good deeds done by a person whilst he is a kaafir will not benefit him in the Hereafter at all, because Allaah says (interpretation of the meanings):
“And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers” [Aal ‘Imraan 3:85]
“And We shall turn to whatever deeds they (disbelievers, polytheists, sinners) did, and We shall make such deeds as scattered floating particles of dust” [al-Furqaan 25:23]
“Those who deny Our Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) and the Meeting in the Hereafter (Day of Resurrection,), vain are their deeds. Are they requited with anything except what they used to do?” [al-A’raaf 7:147]
‘Aa’ishah (may Allaah be pleased with her) asked the Prophet (peace and blessings of Allaah be upon him) a question similar to that asked here. She (may Allaah be pleased with her) said: “O Messenger of Allaah, during the Jaahiliyyah Ibn Jud’aan used to uphold the ties of kinship and feed the poor. Will that be of any avail to him?” He said, “No, that will not be of any avail to him, because he never said ‘O Lord, forgive me my sins on the Day of Judgement.’” (Narrated by Imaam Muslim – may Allaah have mercy on him) in his Saheeh, 214).
But if the kaafir never heard about Islam and Da’wah never reached him, then Allaah will test him on the Day of Resurrection (please see Question #1244). And Allaah knows best.