Prepare the oven. Preheat to 425°F (220°C). Line a large rimmed baking sheet with parchment paper.
Cut the carrots. Cut into approximately 3-inch lengths, then halve or quarter lengthwise so the pieces have a similar thickness. Keep slender carrots whole for a prettier presentation.
Season and roast. Toss the carrots with the olive oil, salt, and pepper. Spread in a single layer and roast for 25–30 minutes, turning halfway through, until nearly tender and beginning to brown.
Make the glaze. Combine the marmalade, butter, orange juice, Dijon, vinegar, and thyme in a small saucepan. Warm over low heat, stirring until the butter melts and the glaze is smooth.
Glaze the carrots. Pour the glaze over the roasted carrots and toss gently to coat. Spread them back into a single layer and roast for another 8–12 minutes, until tender and glossy. Watch closely toward the end so the glaze doesn’t burn.
Serve. Transfer to a serving platter, spoon any glaze from the pan over the carrots, and finish with extra thyme.