Someone who's uncompromising stubbornly refuses to change their opinions or accommodate other people's ideas. Your mom's uncompromising prohibition on snacks in the living room may keep some friends away from your movie nights.
If you're uncompromising, you don't compromise, or meet people halfway, making some concessions to what they want. Sometimes this is a sign of power and dedication: "Her uncompromising focus on civil rights helped the movement's advance." It can also be evidence of inflexibility and stubbornness: "The President's uncompromising style resulted in many vetoes and little progress."