Alvin York (Gary Cooper) lives far back up in the Appalachian hills of Tennessee, far removed from the modern world of 1916. Eaking out a meager existance, he courts Gracie Williams (Joan Leslie), but finds himself in competition with another man. To win her heart, he set himself the goal of getting a piece of "bottom land', the fertile farmland of the valleys, and much more productive than the washed-out soil of the hills. Local merchant Mr. Tompkins (Erville Alderson) has land he'd be willing to sell, but he'll only give Alvin 60 days to raise the money. Selling all the possessions he can live without, and working himself day and night, he manages to put a few more coins in his little bank every night before he collapses exhausted into his bed.
After two months of hard work, time is running short, and Alvin must do something drastic if he is to get the money he needs before the land is sold to someone else. A local turkey shoot is coming, with a prize beef steer going to the winner. On the day of the contest, Alvin, well known for his marksmanship, takes his turn, and tricks the bird into sticking its head out by imitating a turkey gobble. Firing his trusty flintlock, he get the last turkey of the day. Immediately selling the bird, he buys five chances in the sharpshooting contest that will win the steer. Surprised, none of the other contestants believe Alvin has a chance. "Ain't nobody ever cut five centers, lessen he was Daniel Boone, an' you ain't wearin' no coon-skin cap!" one of the other men tells him. Calmly, Alvin takes his turns, firing his antique gun along with the other men in the contest. He hits the first mark, then the second, then the third. When his fourth turn comes, he makes that one as well, and needs only one more to win the whole prize. The man before him shoots, and cuts the paper target almost exactly. Alvin calmly takes aim and fires, and the whole crowd runs to the targets to see who is the winner. Pastor Pile (Walter Brennan) is the judge, and declares the second man is no more than a hair off, "but Alvin done cut center fair and square!" Alvin is declared the winner.
Alvin again puts his prize up for another contest, and within minutes, he has the money he needs to buy his bottom-land. Triumphantly presenting this to Mr. Thompkins, he is shattered to learn that the land was just sold to someone else. "Your time was rightly up," Alvin is told, "and besides, I never thought you had a chance to win that contest anyhow." With murder in his eye, Alvin stalks off.
Getting good and drunk that night he plots revenge, and despite his friend's pleas, he goes out into the storm to find those who took his land away from him. Lightning strikes a tree as Alvin rides past, and a moment later, another bolt hits the tip of Alvin's gun, blasting it apart, and knocking him clean off his mule. Picking himself up out of the mud, Alvin feels divine intervention has taken a hand, and when he hears singing off in the distance, he stumbles toward it. The local church appears out of the storm, and Alvin goes in. Amazed to see Alvin in his church, Pastor Pile rouses the congregation up into a revival for Alvin's sake, and turns him towards the Lord.
Alvin soon becomes a model Christian, studying the Good Book, and asking forgiveness from Mr. Thompkins, who brandishes a monkey wrench at Alvin when they next meet. Alvin soon works out a deal to share-crop the land he tried to buy, and figures to own it outright within a few years. Miss Gracie also agrees to be a-marriyin' Alvin soon. With his new-found faith, everything seems to going Alvin's way. But trouble is coming; a rider gallops into the little village and declares that the U.S, is at war with Germany. Soon everyone must register for the draft, but Alvin resists due to his beliefs. "War is killin'" he tells the Pastor, "'an' killin' is agin' the Book." Declaring himself a conscientious objector, he appeals against the draft, but is finally forced to join the Army. Dejected and confused, Alvin is told by Pastor Pile that "The war is clear across the ocean, and a lot can happen before you get there. Trust in the Lord Alvin."
In boot camp, Alvin is watched by his Drill Sergeant for trouble, but soon establishes himself as a model recruit. During target practice, Alvin gets a chance to try a modern rifle, and surprises everyone by getting five bulls-eyes in a row during his first try. "That gun shoots a mite to the left," he declares, as if he'd done nothing special. After a few weeks of training, Alvin is summoned to the camp commander's office and questioned about his religious beliefs. Quoting the Bible, the Major tries to show Alvin that it supports fighting for one's beliefs, but Alvin knows the Good Book far better, and turns each of the Major's examples around. Realizing that Alvin is truly a religious man and not simply trying to get out of the Army, he agrees to give Alvin a 2-week furlough to think about his responsibilities. If Alvin still wants out, the Major will agree.
Returning home, Alvin goes up into the hills to think. Wrestling with his duty to either God or Country, a breeze blows his Bible open to a passage in Matthew: "Render unto Caesar that which is Caesar's, and unto God the thing's that are God's." His mind made up, Alvin returns to the Army, and agrees to stay.
His unit ships out to France, and Alvin is soon in the thick of trench warfare. A major push is ordered, and the soldiers go over the top at the appointed minute. Facing withering German machine-gun fire, Alvin's unit tries to flank the enemy, but more and more of them are cut down. When first the commanding officer is wounded, and then the sergeant, Alvin must take command of the few men left. Crawling around the the side of the machine-gun trench, Alvin manages to pick off the German gunners one-by one. Unable to turn their guns to face him, they surrender. Working back behind the enemy trenches, the handfull of American soldiers disarm over a dozen German prisoners, but up on the ridge the machine gunners have noticed what's going on behind them and they turn the guns around to fire on the Americans. Pinned down, York is the only one who can reach the machine guns. Tricking the gunners into exposing themselves by gobbling like a turkey, Alvin picks them off until the entire group is forced to surrender. As they march their prisoners back to the Allied lines, they find that a dozen Americans have captured 132 Germans.
Word quickly spreads of Alvin's heroism, and when the battle is investigated the Army determines that Alvin had shot and killed 25 Germans. When asked about this, Alvin repied that he'd "shot those men in order to prevent them from killin' a whole lot more." Declared a hero, Alvin is awarded the Medal of Honor and the Croix de Gurre. Given a hero's welcome in New York, he is feted by all of high society and given the Key to the City, but all he thinks about is returning to his home in the hills of Tennessee.
Once he finally returns home, he wants to get back to work share-cropping the land and earning the right to call it his. He also askes Miss Gracie to wait for him until he can build a home for them to be married in, but Gracie and the others giggle behind his back, because Alvin still doesn't realize what a famous man he's become. Stopping by the old plot of his coveted bottom-land, Alvin is stunned to see a beautiful new farm built upon it. "It's all for you Alvin," cries Gracie. "The people of Tennessee done built it for you!" With all his dreams come true, Alvin takes Gracie's hand, and they run together to their new home.