The instinct in the moment is usually to just let it go and pick the thread back up later, or never. Do that enough times and the pattern doesn't fix itself, it just becomes the room's default expectation of how meetings with that person work.
The most effective in-the-moment response is calm and short, and it doesn't require calling out the interruption as rude, which usually just escalates things. A simple, level "let me finish this point" or "one more second" holds your ground without making the moment bigger than it needs to be. Said evenly, without a note of frustration in your voice, it reads as confident rather than combative.
", let me just finish this thought, then I want to hear your take." Said calmly, mid-sentence, and then you actually finish the thought before yielding the floor.
If it's a one-time thing, that's usually enough, most interruptions are just enthusiasm or bad timing, not a pattern worth addressing directly. If it's a repeated pattern with the same person, the in-the-moment response only manages the symptom. The pattern itself is worth a direct, private conversation, separate from any specific meeting.
Addressing a pattern in the moment it's happening usually makes it about that meeting. Addressing it privately makes it about the pattern, which is the actual problem.
"I've noticed in a few of our meetings I've gotten cut off mid-point pretty often, I don't think it's intentional, but I wanted to flag it because I want to make sure my input's actually landing. Would you be open to me finishing my thought before you jump in?"
Framing it as wanting your input to actually land, rather than as an accusation about their behavior, tends to get a much better reception, most people genuinely don't realize they're doing it, and a direct, low-drama flag is often all it takes to change the pattern. If it continues after that conversation, that's useful information too: it suggests the interruption isn't accidental, and a firmer, more direct boundary, held consistently, in the room, every time, becomes the next step.
One more thing worth doing regardless: if you notice someone else being repeatedly interrupted in a meeting you're part of, a simple "I don't think they finished" on their behalf is one of the more quietly useful things you can do in a room, for them, and for how the room sees you.