Directed by Clarence Brown, who received six unrewarded Best Director Academy Award nominations throughout his career, with a story by Hugo Butler and Dore Schary, who shared a Best Writing, Original Story Oscar nomination for their work on this one, with a screenplay by Bradbury Foote and Talbot Jennings, this above average biographical drama features Spencer Tracy in the title role as Thomas A. (Alva) Edison. Rita Johnson plays his wife, the former Mary Stillwell, and Lynne Overman plays a longtime friend from the inventor's days as a telegrapher, James J. Cavatt. The rest of the highly recognizable cast of prolific performers includes: Charles Coburn, Gene Lockhart, Henry Travers, Felix Bressart, Byron Foulger, Gene Reynolds, Grant Mitchell, and Paul Hurst. Additionally, Irving Bacon, Harlan Briggs, Jimmy Conlin, Frank Faylen, and Charles Lane are among those who appear uncredited.
The story, told in flashback, begins with Edison (Tracy) arriving in New York to get a job working with someone he knows as a fellow telegraph operator, Cavatt (Overman) nicknamed Bunt. Unfortunately his friend is heading West for other opportunities, but Overman's Uncle Ben Els (Travers) is willing to let him take his nephew's job, helping him with cleaning up the building. Uncle Ben lives in the basement of a business establishment owned by Mr. Taggart (Lockhart), and eventually the tinkerer Edison gets past Taggart's secretary, Edwin Hall (Foulger), when a stock ticker device fails and the future inventor is able to fix it on the spot, to the relief of many anxious businessmen. One of those is an important official with Western Union, General Powell (Coburn), who is intrigued enough with Edison to give him a desk and a job in his laboratory. Edison has several ideas for a better stock ticking device, and many of the workman are assigned to assist him including Michael Simon (Bressart), who was going to be let go until Edison saved his job. While working there, Edison meets his future wife, Mary Stillwell (Johnson), who understands Morse code because she too is a telegrapher. Conlin plays a waiter on their lunch date. When Edison has finally got a device to replace Taggart's inferior stock ticker, Mary suggests that Tom wait until the businessman makes him an offer instead of telling him what he'd thought the invention was worth. In a gloriously amusing scene, Edison ends up getting a check for $40,000 from Powell, after which Taggart gloats that they were prepared to go as high as $60,000 before Edison says he'd have settled for $2,000!
Edison and Mary get married and the inventor uses the money to build and open his own laboratory in Menlo Park, employing all those he'd worked with previously (and more?) under Taggart. Over a five year period, Mary gives birth to a daughter and then a son while Tom and his fellow technicians scrape by with a few other patents. But the business's bills far exceed its income such that Edison is near financial ruin. Uncle Ben and his nephew come for a visit just in time for Bunt to distract the Sheriff (Hurst) from serving his injunctions. Edison has a week to invent something in order to keep the business from going under. Uncle Ben suggests that he work on his incandescent light idea, and the inventor struggles with it non- stop for days while getting grouchy with Mary. But the deadline comes and goes because all of his employees decide to forgo their pay, deciding instead to keep working. Edison had tried to go to Taggart and General Powell for financial assistance, but the General was on his death bed and Taggart wanted too much control in return for a $100,000 investment. It's about this time that Edison begins helping someone who was working on something that the inventor thought was nothing, but this leads to his inventing the voice recording device (e.g. the phonograph). The success of this invention clears up the money woes such that Edison and his men are able to concentrate all their efforts on electric light (e.g. to replace gas), and he hires a young man wanderer that reminds him of himself, Jimmy Price (Reynolds). Before Edison gets too far with this particular problem, his friend Bunt is shown to tell the press prematurely that he'd solved it, which causes bad publicity against the inventor; Lane's character delivers one of these speeches.
After Edison figures out that his incandescent light will only work in a vacuum, hence a glass bulb is needed and, after thousands of experiments, they discover the right material for a filament, the light bulb is invented. After perfecting other details, Edison proposes to light a district within the city free of charge to prove the overall worth of electric light. Naturally Taggart, who owns a lot of gas stock, uses his representative Shade (Mitchell) to make it harder on the inventor - an unrealistic (six month) deadline is proposed and then approved by the city council. However, Edison and his team work to make enough light bulbs, wire the district, and build two dynamos large enough to supply the required electricity and are just about ready a few hours before the deadline before another small detail, regulating the dynamos to work together, must be worked out. Of course, they succeeded in lighting a portion of New York, to the delight of everyone but Taggart. After a montage which lists Edison's other inventions and patents through the years, the story returns to "present day", 1929, on the golden (50 year) anniversary of light (the invention of the light bulb). The soft spoken aged Edison, at a banquet held in his honor, delivers a speech about the evolution of science, how it shouldn't be feared (as apparently it had) because if men can invent it, then they should be able to have the good enough sense to control it.
