He attended Baldwin Senior High School on Long Island where he was a Nassau County and New York state wrestling champion.

When his dream was not attained, Weidman had to decide if he wanted to continue training for the world teams and Olympics or give MMA a shot.

In 2011, Longo and Weidman LAW MMA opened, where they are instructors, owners, and operators in Garden City, New York.

[12] For such a novice fighter to be so aggressive and technical in a pure grappling competition against one of the world's best speaks volumes to what a great MMA middleweight Chris Weidman may become.

[6] Weidman made his MMA professional debut representing the Serra-Longo Fight Team in February 2009 in Louis Neglia's Ring of Combat 23.

[16] His combination of gravity-defying throws, an ironclad base and scarily preternatural grappling skills has already made him one of North America's premier prospects.

Weidman defended the ROC Middleweight Championship on December 3, 2010, at Ring of Combat 33 with an impressive victory over Valdir Araujo via unanimous decision.

[23] Weidman defeated Bongfeldt via first round standing guillotine choke,[24] earning $70,000 "Submission of the Night" honors.

[29] Weidman replaced Michael Bisping on eleven days' notice after Mark Muñoz was forced out of his fight with Chael Sonnen.

[36][37] Bookmakers rated Weidman a 2–1 underdog;[38][39] however, numerous pundits and fighters including long-reigning UFC welterweight champion Georges St-Pierre, picked Weidman to upset the long-reigning middleweight champion:[40][41] I believe it's a bad matchup for Anderson Silva.

This fight will shock a lot of people.As St-Pierre predicted, Weidman knocked out Silva early in the second round with another "Knockout of the Night" performance to become the new UFC Middleweight Champion.

The KO victory gave Weidman the distinction of being the first person to have ever knocked out Silva in a mixed martial arts match.

[50] Silva immediately fell to the mat, forcing referee Herb Dean to stop the fight 1:16 into the second round and give Weidman the victory by TKO.

[51] Low kicks were some of Silva's most effective strikes in their first encounter, which led Weidman to focus on defending against them for the rematch.

[55] After Vitor Belfort withdrew from his title bout at UFC 173, it was announced that Lyoto Machida will next face Weidman.

[60] However, on September 22, it was announced that Weidman had suffered a broken hand and the bout was again rescheduled to take place on February 28, 2015, at UFC 184.

[64] After surviving an initial flurry of punches from Belfort, Weidman secured a takedown, went into the mount position, and won the fight via TKO due to strikes in the first round.

[66] In the fourth defense of his title, Weidman faced Luke Rockhold on December 12, 2015, in the co-main event at UFC 194.

After taking damage Weidman survived until the fourth round where Rockhold again took him down and continued his ground and pound success which ultimately led to a fourth-round TKO stoppage by the referee Herb Dean.

Weidman appeared emotional and said at the post-fight press conference that the doubts and negative comments which he received during his three-fight losing streak were tough on him and his family and he was happy to be back in the game.

[78] Weidman's light heavyweight debut took place on October 18, 2019 at UFC on ESPN 6 against Dominick Reyes in the main event.

[81] However, on April 9, Dana White, the president of UFC announced that this event was postponed to a future date and the pairing was scrapped.

[85] However, Weidman was pulled from the event due to a positive COVID-19 test and the bout was cancelled,[86] The rematch took place at UFC 261 on April 24, 2021.

Weidman immediately fell to the mat, with referee Herb Dean calling a stop to the fight and declaring Hall the winner via technical knockout.

He announced the following day that doctors had informed him that he would be unable to walk without crutches for eight weeks, and would need a recovery period of between six and twelve months before he could resume mixed martial arts training.

However, the result would immediately be overturned to a technical decision win for Weidman due to him poking Silva in both eyes during the finishing sequence.

[103] On January 25, 2025, it was reported that Weidman had been drafted on the New York Team of the 2025 season for startup mixed martial arts organization Global Fight League.

[105] Weidman won the ADCC East Coast Trials in 2009 and earned an invitation to that year's world championships.

He competed at 88kg and lost on points to André Galvão in the opening round, before being submitted by Vinny Magalhães in the absolute division.

Weidman was booked to compete against ADCC veteran and Judoka Owen Livesey in the main event of Polaris 23 on March 11, 2023.