Weather in the end of June

The most accurate weather forecast will be available just a couple of days before you leave, so don't forget to check. Let's assume the average means a range from 63 to 83, with plenty of days at 83. I can recall that several past Junes were reported as "heat waves" in Europe, not fitting the average. Also, temps can feel higher when the heat is radiating off the concrete all around than if you're in a grassy field. But luckily, most museums are air conditioned.

Good advice to check a live weather channel for Paris one or two days before departure. The reason for this is that weather systems can and do blow through very suddenly.
Expect it to be warm with maybe some light rain. It will be warm at night, so hope you'll have air conditioning where you're staying.

It was nearly 100F late June last year in Paris. And we didn't have air conditioning.

Thank you for your responses. I knew it would be hotter than 70 degrees, but just wanted some first hand knowledge. I just hope and pray it doesn't hit 100!

It probably won't reach 100F, but could reach 85 - 90 F.
I wouldn't bring heavy jeans, for example.

All the times I've been to Paris at the end of June, (or the month of June as a whole), it was very warm to hot. Expect it to be hot.

It can vary greatly. Two times I've had to hunt down sweaters or jackets to buy in late June. Another time the weather turned overnight from cool to very hot and stayed that way. Another time when I lived in Paris, we didn't see sun in the summer for four years, but those years were bookended by very warm summers. So bring layers and don't assume anything is typical as it changes a lot and quickly.

We were in Paris in early July two years ago. The first several days it was very warm and humid (at least by our standards), but the last day when we took a bike tour at Versailles, it rained and was quite cool. We also went to the top of the Eiffel Tower that evening and it was windy and somewhat chilly. Always good to have that light jacket with you!