Can an indulgence be applied to a deceased non-Catholic Christian? The Manual of Indulgences published by the United States Conference of Catholic Bishops states that

The faithful can obtain a partial or plenary indulgences for themselves, or they can apply them to the dead by way of suffrage.

As far as I know, the Catholic Church acknowledges that deceased non-Catholic Christians can go to Purgatory (e.g. this post mentions that Anne Catherine Emmerich had visions of Protestants in Purgatory) so in theory such non-Catholic Christians would be eligible to have indulgences applied to them. Indeed, the Manual of Indulgences describes indulgences as a remission of temporal punishment for sins for a &quot;properly disposed member of the Christian faithful&quot; (as opposed to only the Catholic faithful):

An indulgence is a remission before God of the temporal punishment for sins, whose guilt is forgiven, which a properly disposed member of the Christian faithful obtains under certain and clearly defined conditions through the intervention of the Church, which, as the minister of Redemption, dispenses and applies authoritatively the treasury of the expiatory works of Christ and the saints.

However, the description of an indulgence indicates that it is the Church which dispenses and applies indulgences, so it seems possible that the Church might choose to withhold the dispensing and application of indulgences to certain souls in Purgatory (e.g. Protestants who might have been anti-Catholic in life). Moreover, it's not clear what is considered a &quot;properly disposed member&quot; of the Christian faithful -- perhaps non-Catholic Christians might not be considered &quot;properly disposed&quot; and thus not eligible to have indulgences applied to them.1
Has the Catholic Church explained whether or not indulgences can be obtained for non-Catholic Christians in Purgatory? If so, are there any limitations (e.g. perhaps only souls from certain denominations are eligible, similar to how only Christians of certain denominations are permitted to receive Communion)?

1I suspect the meaning of &quot;properly disposed&quot; refers to the norm that

§1. In order to be capable of gaining indulgences one must be baptized, not excommunicated, and in the state of grace at least at the completion of the prescribed works.
§2. To gain an indulgence, one must have at least the general intention of doing so and must carry out the enjoined works at the stated time and in due fashion, according to the sense of the grant.

However, since I don't see a definition of exactly what &quot;properly disposed&quot; means I can't rule out the possibility that one must be Catholic to be &quot;properly disposed&quot;.
Can an indulgence be obtained for a deceased non-Catholic Christian?
The short answer is possibly and even probably.
There are several reason, why I believe that yes indulgences may be applied to souls that were non-Catholic Christians in this life, but are now in purgatory and are converted.
Not wanting to politicalize this question, I would simply like to bring up a certain point to start off with. Masses are offered for any number of reasons and this includes Masses being offered for the conversion of a particular Protestant of simply for their intentions. Can not tell you how many times I have read the Mass intention listed in our parish bulletin for the intentions of a certain Donald Trump. We all know the the former President of the United States is not Catholic, yet the intentions of the Sacrifice of  Mass have been offered for him.
Being in purgatory presumes that non-Catholic Christians that they have been converted and as a result can reside in purgatory, just like Catholics.
Anne Catherine Emmerich has the following to say on the subject:

I was present when God passed sentence on notorious sinners. Great is His justice, but still more inconceivable is His mercy. He damns only those who are determined not to be converted; they who have a spark of good will are saved... I have seen in Purgatory Protestants who were pious in their ignorance; they are very desolate, for no prayers are offered for them... I saw that by our prayer and suffering, many a soul who labours not during life, can be converted and saved at the hour of death. - Purgatory for those who are saved outside the Church?

Some of these messages given to Catherine Emmerich were, 'that every parish and diocese, each city and country has its own particular and powerful guardian angel.' This Catholic mystic was to see and be told many things including these messages from Heaven, She revealed that to gain an indulgence we must approach the Sacraments with true repentance and a firm purpose of amendment or we do not gain it. She deposes that it is more holy to pray for the Poor Souls in Purgatory than for sinners who are still alive, for Anne had a particular love and devotion for the poor souls in Purgatory. She was also told that 'more Protestant souls stayed in Purgatory the longest not because they were worse than anyone else, but because so few people prayed for the repose of their souls or offered up Masses for their soul.'
Being in purgatory, means that these poor souls are converted and thus I would lean towards the possibility that an indulgence can be applied to a deceased non-Catholic Christian?
Now an indulgence can only be gained by a practicing Catholic under certain conditions. However the Church does not stipulate as who may be the receive an indulgence when applied to the faithful departed when applied to the souls in purgatory.

The Gift of the Indulgence

To gain indulgences, whether plenary or partial, it is necessary that the faithful be in the state of grace at least at the time the indulgenced work is completed.

A plenary indulgence can be gained only once a day. In order to obtain it, the faithful must, in addition to being in the state of grace:


— have the interior disposition of complete detachment from sin, even venial sin;
— have sacramentally confessed their sins;
— receive the Holy Eucharist (it is certainly better to receive it while participating in Holy Mass, but for the indulgence only Holy Communion is required);
— pray for the intentions of the Supreme Pontiff.



Visit to a Cemetery (Coemeterii visitatio)

An indulgence, applicable only to the Souls in Purgatory, is granted to the faithful, who devoutly visit a cemetery and pray, even if only mentally, for the departed. The indulgence is plenary each day from the 1st to the 8th of November; on other days of the year it is partial. - The Enchiridion Of Indulgences

A soul in purgatory is a soul in purgatory. No where does the Church define that an indulgence for particular soul in purgatory has to be named in order to receive an indulgence when we meet the requirements on their behalf. Thus the faithful may apply an indulgence to a particular member of their family, any soul in purgatory or even for the poorest soul in purgatory.
There are more ways to relieve the sufferings of the souls in purgatory than obtaining an indulgence in order to release them from their pains. Obtaining an indulgence for them is very common, especially during November. I was taught in the seminary that when we pray for a particular soul in purgatory and that that soul is no longer in need of our prayers that God will apply the merits to another soul in need. Prayer is never in vain.