Salvation is believed to be a process that begins when a person first becomes a Christian, continues through that person’s life, and is completed when they stand before Christ in judgment. Therefore, the faithful Christian can say in faith and hope, “I have been saved; I am being saved; and I will be saved.”

Do Jehovah’s Witnesses believe that they are the only persons who will be saved?

What JW.org says…
…about being Saved

No. Many millions who lived in centuries past and who weren’t Jehovah’s Witnesses will have an opportunity for salvation. The Bible explains that in God’s promised new world, “there is going to be a resurrection of both the righteous and the unrighteous.” (Acts 24:15) Additionally, many now living may yet begin to serve God, and they too will gain salvation. In any case, it’s not our job to judge who will or won’t be saved. That assignment rests squarely in Jesus’ hands.—John 5:22, 27.

What AvoidJW.org says…
…about being Saved

Read again what JW.org says about being saved: “millions who lived in centuries past…will have an opportunity for salvation”.  Jehovah’s Witnesses are a relatively new religion. It was founded in 1870. Therefore, they have to admit that millions who lived centuries ago have an opportunity to be saved. After all, it was impossible for those of old to become Jehovah’s Witnesses when the religion never existed! The reality is, their answer to the question asked in this post title is “Yes”. They really do believe that one must serve God within the Jehovah’s Witness faith to gain salvation. Although, they say it is not their job to judge, they do judge (see Are Former Jehovah’s Witnesses Shunned?).

Let’s ask the question again: Will only Jehovah’s Witnesses be Saved? Yes. Since 1870. Or at least, that is what Jehovah’s Witnesses believe.