The team started the season poorly and were near the bottom of the league table after six games, but won five times in October to move into the top half, where they remained at the end of 1983.

The highest attendance recorded at the club's home ground, Priestfield Stadium, was 17,817 for the second of the two replays against Everton.

[7] Before the new season, Gillingham signed two new players: John Leslie, a forward, arrived from Wimbledon,[8] and David Fry, a goalkeeper, joined the club from Crystal Palace, both on free transfers.

[9] Peacock also attempted to sign another forward, Mike Barrett, but although his club, Bristol Rovers, accepted Gillingham's proposed transfer fee, the player chose to reject the move.

[17] The first league game of the season at Gillingham's ground, Priestfield Stadium, took place a week later against Hull City.

[30] A week later, Terry Cochrane, a winger newly signed on loan from Middlesbrough,[31][32] made his debut and scored the first goal in a 2–0 victory at home to Preston North End.

[41][42] In the next game, against Rotherham United, Gillingham took a 2–0 lead through goals from Weatherly and Mehmet but were reduced to ten men shortly before the end of the first half when Johnson was sent off.

[44] Gillingham began December with a 1–0 win away to Port Vale, Cochrane scoring the only goal of the game less than a minute from the start.

[15] On Boxing Day, Gillingham achieved their biggest win of the season with a 5–1 victory at home to Southend United.

[37][47] Gillingham ended 1983 with two defeats, losing 3–0 away to Bristol Rovers and 1–0 at home to Wimbledon on 31 December, the first time they had lost at Priestfield since mid-September.

[54] They secured a 3–2 win away to Brentford on 4 February and, despite conceding a goal inside the first minute, continued their unbeaten run a week later by beating AFC Bournemouth 2–1.

[15] At the end of the month, Gillingham were 10th in the table, seven points below the top three places which would result in promotion,[57] but still with the advantage of having played up to four fewer games than all the teams above them.

[64] Phil Cavener, making his first appearance in the starting line-up, scored a goal inside the first minute and Gillingham won 1–0.

[68] In the last game of March, goals from Leslie and Mehmet, neither of whom had scored for over a month, and Cascarino secured a 3–1 win over Orient;[15] despite the victory, Gillingham were again 13 points below third place.

[69] A goal from Cascarino gave Gillingham a second consecutive win as they beat Bolton Wanderers 1–0 on 7 April,[70] but it would prove to be the only victory they achieved in eight matches during the month.

[80] Two days later, Gillingham conceded a goal against second-placed Wimbledon just ten seconds after the start of the match, but came back to win 3–1.

[85] A goal from Phil Handford gave Gillingham a 1–0 victory at Leamington's Windmill Gound and took them into the second round, where they faced another Southern League team, Chelmsford City, at Priestfield.

[87] Gillingham's third round opponents were fellow Third Division team Brentford; with less than 15 minutes of the match at Priestfield remaining, Brentford were winning 3–1 and seemed set for victory, but Gillingham scored four goals in the final 11 minutes to secure a 5–3 win and reach the fourth round (last 32) of the competition for only the third time in the club's history.

The match took place at Everton's ground, Goodison Park, and Gillingham held their higher-level opponents to a goalless draw, meaning that a replay at Priestfield was required.

[90][91][92] In a review of Cascarino's autobiography, published sixteen years later, Dave Hill of the magazine When Saturday Comes described the moment as "one of the great misses [of all time]";[93] in the book Cascarino himself attributed it to a sudden attack of self-doubt at the crucial moment, writing "Panic was clouding my brain like a fog.

The reporter for The Daily Telegraph wrote that Gillingham's decision after winning the coin toss for the choice of ends to play with a strong wind behind them in the first half backfired as it led to them relying too much on long-range shots which lacked accuracy.

[99] The second leg took place two weeks later at Stamford Bridge and resulted in a 4–0 victory for Chelsea, making the aggregate score 6–1 and eliminating Gillingham from the competition.

[105] With three minutes of the additional period remaining, 17-year old Teddy Sheringham scored to give Millwall a 4–3 win, meaning that Gillingham were eliminated from the tournament.

[108] Having attracted the attention of several First Division clubs with his performances, the defender left Gillingham at the end of the season to join Norwich City for a fee of £135,000.

[111] The following season, Gillingham matched their best performance since returning to the Third Division, finishing fourth and missing out on promotion by one place.