Samuel William Alvey was born and raised in Waterford, Wisconsin. Alvey competed in football and wrestling at Waterford High School. He gained his interest in martial arts from watching World Wrestling Federation (now WWE) events, Jackie Chan movies, and Teenage Mutant Ninja Turtles. Alvey attended Lakeland University in Plymouth, Wisconsin. It was around that this time that Alvey began competing in international pankration events. Alvey transitioned to mixed martial arts in the mid 2000s and would compile a 6-1 amateur record. He lives Southern California with his wife and five children.

Alvey made his professional debuting 2007, compiling a record of 19-4 with 1 NC fighting in local talent in Wisconsin. Alvey  competed across 3 different divisions Light Heavyweight, Middleweight, and Welterweight (TUF). He fought for King of the Cage 4 times. 3 of those were wins, along with 1 draw. The most notable fight from this period in Alvey's career was a loss to future UFC Middleweight Gerald "GM3" Meerschaert. In 2010, Alvey would move to Temecula, California to train with Dan Henderson at Team Quest (now Dan Henderson Fitness Center).

Alvey made his way to Bellator and competed in the Middleweight Season 5 tournament. In his debut he beat Karl Amoussou via split decision (Bellator 45). In the quarter final he lost to Vitor Vianna via split decision (Bellator 50). After the loss to Vitor Vianna he went on to win 4 of 5 fights. He then joined the cast of The Ultimate Fighter Season 16. This is where he would drop to Welterweight for the first time in his career. To get into the house he fought Leo Kuntz, knocking out Kuntz  with a single right hook to end the fight. Shane Carwin selected Alvey with his first pick. Carwin picked Sam Alvey to go up against  Team Nelsons, Joey Rivera. After a domination by Joey Rivera he ended up winning the unanimous decision win over Sam Alvey. After being eliminated Sam Alvey confirmed he would be moving back to Middleweight saying this:

"Most of my career I’ve been at 205 and then I made the cut to 185 and that was a pretty big cut. Then 29 days before the show aired I got asked to be on the show, so I cut 40lbs in that 29 days. I was so drained after the cut and I just never regained, I mean in the fight I threw three punches, I had two takedowns or what could have been takedowns had I used it, it just wasn’t my day."

Alvey would return to the regional circuit after his TUF loss, where he would defeat Jason South via fifth round TKO to claim the Maximum Fighting Championship Middleweight Championship (MFC 38). He defend this belt once (MFC 40) before avenging his loss to GM3 via unanimous decision (NAFC: Mega Brawl).

Alvey made his UFC debut on August 16, 2014 at UFC Fight Night: Bader vs. St. Preux. He lost to Tom Watson via unanimous decision. Alvey would KO/TKO his next three opponents, including a Performance of the Night win against Cezar Ferreira (UFC Fight Night: Bigfoot vs. Mir). After losing to Derek Brunson by TKO (UFC Fight Night: Teixeira vs. Saint Preux) and Elias Theodorou by unanimous decision (UFC Fight Night: MacDonald vs. Thompson), Alvey would go on a four fight win streak which culminated with a unanimous decision win over former Strikeforce and Pancrase Champion Nate Marquardt (UFC on Fox: Shevchenko vs. Peña).

Alvey's fight against Thales Leites (UFC Fight Night: Swanson vs. Lobov) was his fortieth professional MMA bout. He lost via unanimous decision. Alvey would defeat TUF Season 2 winner and former UFC Light Heavyweight Champion "Suga" Rashad Evans via split decision in his very next fight (UFC Fight Night: Pettis vs. Moreno). Nevertheless, Alvey showed inconsistency in his next bout by missing weight and dropping a unanimous decision to Ramazan Emeev (UFC Fight Night: Cowboy vs. Till).

After the Emeev fight, Alvey breifly moved up to Light Heavyweight. He would KO Marcin Prachnio (UFC on Fox: Emmett vs. Stephens) and defeat Gian Villante (UFC Fight Night: Rivera vs. Moraes) via split decision before facing PRIDE and UFC veteran Antonio Rogerio "Lil Nog" Nogueira at UFC Fight Night: Santos vs. Anders. Nogueira swarmed Alvey in the second round and TKO'd him. 

The Nogueira fight initiated the steep decline in Alvey's career and led to the most infamous streak in UFC history. Smilin Sam would go 0-9-1 in his final ten fights, creating a winless streak that is unlikely to be surpassed. Alvey would lose his next three fights to UFC newcomers Jimmy Crute (UFC 234)(TKO), Klidson Abreu (UFC on ESPN: dos Anjos vs. Edwards)(UD), and Ryan Spann (UFC 249)(split decision). In the Crute loss, Alvey immediately began arguing the stoppage with referee Marc Goddard. Alvey would then fight to a split draw against Da Un Jung (UFC 254).

Alvey returned to Middlweight in 2021, where he was choked unconscious by Julian Marquez in a Fight of the Night bout at (UFC on ABC: Vettori vs. Holland). Alvey's next loss was arguably his most humiliating: he dropped a split decision to Wellington Turman despite the fact that Chris Tognoni deducted two points from Turman in the third round for repeated eye pokes. Adalaide Byrd scored it 28-27 Alvey, while Derek Cleary and Ron McCarthy scored it 28-27 Turman. Alvey was finished in his last two fights, losing to Brendan Allen via rear naked choke (UFC Fight Night: Hermansson vs. Strickland), and getting TKO'd in a one-sided beating in front of his children by Michał "Hussar" Oleksiejczuk (UFC on ESPN: Santos vs. Hill).