Christmas Eve in Paris

Stephen,
Ste. Chapelle is no longer an "operating" church. It was "decommissioned." You can go to mass times.org to find out times of masses worldwide, but I doubt if any services for Christmas will be online this soon. You could probably find each church's website to email them with questions, but maybe only in French.
If I had to choose, I would like to attend Ste. Sulpice because of the organ's reputation. However, many churches in Paris are known for their music, choirs, etc.
In the Catholic church, many parishes have moved midnight services up to 10:00 p.m. At least in the US.

Bonne chance!

Sounds really lovely to attend a service anywhere in Paris on Christmas Eve. Notre Dame Cathedral will be reopening on December 8, 2024 with special celebrations through June 8, 2025. Maybe there will be something special held on Christmas Eve. (I assume a midnight mass, but with the reopening, perhaps there are other events as well.)

Of course there's midnight mass at Notre Dame de Paris, but also in the other churches around town.
In France families celebrate with a festive meal. Those who go to church eat after midnight mass.
Be sure to book a restaurant if you want to eat. You can catch up on your sleep in the plane the 25th.

We did Notre Dame years ago and it was magical.... It's "suppose' to be open this year by then If you do chose that get there EARLY, it was packed when we went and with it being the first holiday after the fire.... I bet it's a popular event!

We will also be in Paris on Christmas eve and plan to attend Mass at Notre Dame. I recently found this information.

“The first Notre Dame Christmas Eve Masstakes place on December 24 at 4:30pm, followed by a Family Mass at 6pm, Vespers at 8pm, and an organ concert from 10:30pm-11pm.  Following the concert, the Cathedral's Midnight Mass begins at 11pm. 
You should expect long lines for admission, particularly for the concert and Midnight Mass.  Tickets are not required, but to get through a security at the entrance and find a seat, you should arrive at least 2-3 hours early.”

If waiting in line is not for you we have attended Christmas Mass at Church of Saint-Germain-des-Prés and Church of Saint-Eustache and both were beautiful and special.

You didn’t ask, but I’m suggesting it anyway. We had our Xmas Eve dinner on Bustronome. We were served a nice meal while being driven around the city (very slowly). It was a beautiful evening.

Thanks everyone!