Stieber initially played for Budapest-based Goldball '94 alongside younger brother András, before moving to Hungarian giants Újpest.

He had an unsuccessful trials with Arsenal and Manchester United prior to signing a youth contract with Aston Villa where he played for four years.

[1] Stieber signed a two-year contract with Aston Villa in May 2005 and quickly impressed Tony McAndrew with his performances for the Academy.

He was part of the squad that got to the Play-offs Final of the FA Premier Academy League in May 2006, which Villa lost 3–2 against Southampton.

Stieber appeared 13 times for Aston Villa Reserves in the 2006–07 season, scoring two goals, against Fulham and Chelsea.

[1] In late May 2007, Stieber guided Aston Villa to success in the 2007 HKFC Philips Lighting International Soccer Sevens, scoring a spectacular winner against City Academy Hong Kong to book a place in the knock-out stages.

He then went on to lead the Midlands club to victory against Urawa Red Diamonds, PSV and finally Central Coast Mariners FC to secure the trophy, in a competition which has brought notable success to Aston Villa in the past.

His efforts in the competition were also rewarded with the Player of the Tournament trophy – succeeding last years winner – Gabriel Agbonlahor.

After this success, he was rewarded with a three-year contract at Aston Villa – the longest given to any of the seven contractee's – thus showing the promise and potential shown in the young Hungarian.

In July 2007, Stieber was given his first taste of first-team action, when he was called up to the senior squad for the tour of the U.S. and Canada.

He made his debut against Toronto and impressed against the Major League Soccer team, he also appeared in a further pre-season match against Walsall, in which he assisted the first goal of the game.

[3] Despite not making a competitive breakthrough to the senior team, he made a positive impression for Aston Villa Reserves that season, scoring against Fulham and Portsmouth and chalking up 6 assists in the opening 6 matches.

In early July 2008, he was called up to a 21-man squad for the tour of Switzerland, but only played 20 minutes – all in the 6–0 victory over FC Wil 1900.

[4] Upon joining the club, Manager Russell Slade commented on Stieber, attributing his style on ‘dead-ball situations and a great crosser of the ball.’[5] Stieber made his Yeovil Town debut two days later on 24 November 2007, in a 2–1 loss against Millwall[6] and scored his first goal days before his loan spell ran out, in the 2–1 victory over Brighton & Hove Albion.

[8][9] However, Stieber suffered a thigh injury in training[10] and made his return to the first team on 29 March 2008, in a 0–0 draw against Bristol Rovers, which turns out to be his last appearance.

[25] Stieber made his Alemannia Aachen debut, in the opening game of the season, where he set up one of the goals, in a 2–2 draw against Union Berlin on 20 August 2010.

[45] Stieber made his Greuther Fürth debut, in the opening game of the season, where he came on as a substitute for Sebastian Tyrała in the 69th minute, in a 3–0 loss against Bayern Munich.

[54] At the start of the new season, Stieber performed strongly, as he had 3 goals and 6 assists in just 9 games, where he scored twice against Union Berlin[55] and once against Dynamo Dresden, where he provided a hat–trick in an eventual 4–0 win.

[68][69] On 7 February 2015, he set the record of the highest distance in the 2014–15 Bundesliga by running 13.9 km against Hannover 96 at the Imtech-Arena, Hamburg.

[75][76] Stieber made his first appearance of the 2015–16 season, where he came on as a substitute for Nicolai Müller in the 87th minute, in a 1–0 win over 1899 Hoffenheim on 23 October 2015.

[79] Stieber explained his decision to leave Hamburg, citing first team football in hopes of making to the Hungary squad for the UEFA Euro 2016.

[84] Two days later, on 14 August 2016, Stieber made his Kaiserslautern debut, in the opening game of the season, where he played 26 minutes, in a 1–1 draw against Würzburger Kickers.

[85] Six days later on 20 August 2016, Stieber scored his first Kaiserslautern goal in the first round of DFB Pokal, in a 4–3 loss against Hallescher FC after the game went extra time.

After D.C. United was able to improve and get their new stadium, Audi Field in 2018, Zoltan managed to score 5 goals and 7 assists in the 2018 season.

In June 2019, Stieber told a reporter that he desired to leave D.C. United in order to get more chances with the Hungary national team.

[90] At the end of the 2021–22 season, MTK was relegated to the second-tier NB II, and Stieber made his debut on that level.