He spent time on loan at Welling United, Accrington Stanley and Gillingham before making his Charlton debut in the last match of the 2006–07 season.

Despite the club's relegation from the Premier League, he was unable to cement a regular starting position, and had two loan spells during 2008, at Bury and at Hereford United.

He played regularly for Motherwell over three years, then returned to England to join Birmingham City, for whom he missed only one Championship match in two seasons.

[7] As a youngster, Randolph spent a month on loan at Conference South club Welling United in 2004; he played four league matches and once in the FA Cup.

Replacing loanee Scott Carson, who was ineligible to play against his parent club, Randolph performed well, limiting Liverpool to two goals, one of which was a penalty kick in the 90th minute for a 2–2 draw.

[14] He started Charlton's next match, at home to Southampton, and contributed to a farcical own goal when he appeared to catch a high ball, then dropped it into the net via teammate Paddy McCarthy.

[17] On 11 November 2008, it came to light that Randolph had refused to play in an FA Cup match against Dagenham & Redbridge, amid speculation that another goalkeeper would be joining Hereford.

[20] In response, Randolph expressed his unhappiness with Turner's statement, and received support from Charlton manager Alan Pardew.

Despite "a string of stunning first half saves", the Conference North team won 1–0 to inflict what the local newspaper described as the "most embarrassing defeat in the club's 104-year history".

[25] Randolph regained his starting place in March 2010 after Elliot was injured, and kept it for the remainder of the season, including the play-offs, in which Charlton lost on penalties to Swindon Town in the semi-finals.

[26] Although Charlton offered Randolph a new contract,[27] he chose instead to join Scottish Premier League club Motherwell on 1 July 2010 on a free transfer.

[30] Randolph established himself as first-choice goalkeeper; in his first season, he broke John Ruddy's club record of 15 clean sheets on 27 February 2011 in a 2–0 win over Celtic.

[35] Because 2011–12 runners-up Rangers entered administration, they were ineligible for UEFA competitions, so Motherwell's third-place finish earned the club entry into the Champions League for the first time.

[41] Together with teammates Shaun Hutchinson, Nicky Law and Michael Higdon, Randolph was named in the 2012–13 PFA Scotland Team of the Year.

[43] With Randolph's contract due to expire at the end of the season, Motherwell manager Stuart McCall said in mid-April that there was only a "slim possibility" of keeping him at the club.

[43] He went straight into the starting eleven, made his debut in a 1–0 defeat at home to Watford on 3 August, and remained ever-present in Championship matches throughout the season, though Colin Doyle played in all Birmingham's cup ties.

[46] The unbroken run continued into the next season, until Randolph was sent off late in the home defeat to Bolton Wanderers on 18 October 2014 for bringing down Craig Davies (who missed the ensuing penalty), so was suspended for the next match.

[48] Manager Gary Rowett said that had a Premier League club made a bid for Randolph's services in the January transfer window, he would not have stopped him leaving, but he wanted to keep him at Birmingham.

[49] The club confirmed in May that he had rejected the offer of a contract extension, and would leave as a free agent under the Bosman ruling at the end of his existing deal.