It is often said that Lasker used a "psychological" approach to the game, and even that he sometimes deliberately played inferior moves to confuse opponents. However, recent analysis indicates that he was ahead of his time and used a more flexible approach than his contemporaries, which mystified many of them. While it is often said that Lasker spent little time studying the openings, he actually knew the openings well but disagreed with many contemporary analyses. Although Lasker also published chess magazines and five chess books, later players and commentators found it difficult to draw lessons from his methods.

He demanded high fees for playing matches and tournaments, which aroused criticism at the time but contributed to the development of chess as a professional career. The conditions which Lasker demanded for World Championship matches in the last ten years of his reign were controversial, and prompted attempts, particularly by his successor José Raúl Capablanca, to define agreed rules for championship matches.

Lasker also made other contributions to the development of other games. He was a first-class contract bridge player and wrote about this and other games, including Go and his own invention, Lasca. His books about games in general presented a problem which is still considered notable in the mathematical analysis of card games. Lasker was also a research mathematician who was renowned for his contributions to commutative algebra, as he defined the primary decomposition property of the ideals of some commutative rings when he proved that polynomial rings have the primary decomposition property. On the other hand, his philosophical works and a drama that he co-authored receive little attention today.

Emanuel Lasker was born on December 24, 1868 at Berlinchen in Neumark (now Barlinek in Poland), the son of a Jewish cantor. At the age of eleven he was sent to Berlin to study mathematics, where he lived with his brother Berthold, eight years his senior, who taught him how to play chess. According to the website Chessmetrics, Berthold was among the world's top ten players in the early 1890s. To supplement their income Emanuel Lasker played chess and card games for small stakes, especially at the Café Kaiserhof.

Emanuel Lasker shot up through the chess rankings in 1889, when he won the Café Kaiserhof's annual Winter tournament 1888/89 and the Hauptturnier A ("second division" tournament) at the sixth DSB Congress (German Chess Federation's congress) held in Breslau. He also finished second in an international tournament at Amsterdam, ahead of some well-known masters, including Isidore Gunsberg (assessed as the second strongest player in the world at that time by Chessmetrics). In 1890 he finished third in Graz, then shared first prize with his brother Berthold in a tournament in Berlin. In spring 1892, he won two tournaments in London, the second and stronger of these without losing a game. At New York 1893, he won all thirteen games, one of the few times in chess history that a player has achieved a perfect score in a significant tournament.

His record in matches was equally impressive: at Berlin in 1890 he drew a short play-off match against his brother Berthold; and won all his other matches from 1889 to 1893, mostly against top-class opponents: Curt von Bardeleben (1889; ranked 9th best player in the world by Chessmetrics at that time), Jacques Mieses (1889; ranked 11th), Henry Edward Bird (1890; then 60 years old; ranked 29th), Berthold Englisch (1890; ranked 18th), Joseph Henry Blackburne (1892, without losing a game; Blackburne was aged 51 then, but still 9th in the world), Jackson Showalter (1892–1893; 22nd) and Celso Golmayo Zúpide (1893; 29th). Chessmetrics calculates that Emanuel Lasker became the world's strongest player in mid-1890, and that he was in the top ten from the very beginning of his recorded career in 1889.

In 1892 Lasker founded the first of his chess magazines, The London Chess Fortnightly, which was published from August 15, 1892 to July 30, 1893. In the second quarter of 1893 there was a gap of ten weeks between issues, allegedly because of problems with the printer. Shortly after its last issue Lasker traveled to the USA, where he spent the next two years.

Lasker challenged Siegbert Tarrasch, who had won three consecutive strong international tournaments (Breslau 1889, Manchester 1890, and Dresden 1892), to a match. Tarrasch haughtily declined, stating that Lasker should first prove his mettle by attempting to win one or two major international events.

Rebuffed by Tarrasch, Lasker challenged the reigning World Champion Wilhelm Steinitz to a match for the title. Initially Lasker wanted to play for US $5,000 a side and a match was agreed at stakes of $3,000 a side, but Steinitz agreed to a series of reductions when Lasker found it difficult to raise the money. The final figure was $2,000, which was less than for some of Steinitz' earlier matches (the final combined stake of $4,000 would be worth over $495,000 at 2006 values). Although this was publicly praised as an act of sportsmanship on Steinitz' part, Steinitz may have desperately needed the money. The match was played in 1894, at venues in New York, Philadelphia, and Montreal. Steinitz had previously declared he would win without doubt, so it came as a shock when Lasker won the first game. Steinitz responded by winning the second, and was able to maintain the balance through the sixth. However, Lasker won all the games from the seventh to the eleventh, and Steinitz asked for a week's rest. When the match resumed, Steinitz looked in better shape and won the 13th and 14th games. Lasker struck back in the 15th and 16th, and Steinitz was unable to compensate for his losses in the middle of the match. Hence Lasker won convincingly with ten wins, five losses and four draws. Lasker thus became the second formally-recognized World Chess Champion, and confirmed his title by beating Steinitz even more convincingly in their re-match in 1896–1897 (ten wins, five draws, and two losses).

Influential players and journalists belittled the 1894 match both before and after it took place. Lasker's difficulty in getting backing may have been caused by hostile pre-match comments from Gunsberg and Leopold Hoffer, who had long been a bitter enemy of Steinitz. One of the complaints was that Lasker had never played the other two members of the top four, Siegbert Tarrasch and Mikhail Chigorin – although Tarrasch had rejected a challenge from Lasker in 1892, publicly telling him to go and win an international tournament first. After the match some commentators, notably Tarrasch, said Lasker had won mainly because Steinitz was old (58 in 1894).