He then produced a match-winning performance against Rangers at Ibrox on 2 January 2011. He was selected as a lone striker and scored both Celtic goals in a 2–0 victory. His first goal came from latching onto a Joe Ledley pass before rounding Rangers goalkeeper Allan McGregor and slotting home from a wide angle. His second came after he won a penalty which he converted to secure the victory. His efforts in this game won him Goal.com's World Player of the Week Award. In the following game, a Scottish Cup tie against Berwick Rangers, Samaras again started but failed to last the 90 minutes after sustaining a hamstring injury. Samaras had an influential performance in a 3–0 home victory against Rangers in the SPL on 20 February, helping to set up the second goal for Gary Hooper and causing problems for the opposition throughout the game.
On 16 March, Samaras captained Celtic for the first time in a 2–1 Scottish Cup win over Inverness Caledonian Thistle at the Caledonian Stadium. Two days later, he signed a new deal to keep him at Parkhead until the summer of 2014. Celtic drew 0–0 with Rangers on 24 April 2011 in the final Old Firm league fixture of the season, with Samaras missing a penalty kick late in the second half. The draw kept Rangers one point ahead of Celtic in the league, and the Ibrox club went on to win the league by one point despite Celtic's emphatic 4–0 win over Motherwell in the final league game of the season (Samaras scoring Celtic's second goal in that game). Samaras did end the season with silverware though, playing a week later in Celtic's 3–0 win over Motherwell in the Scottish Cup Final.
On 3 November 2011, Samaras started against Rennes in a Europa League match at Celtic Park. Celtic won the match 3–1 with Samaras getting two assists. He drew plaudits for his much noticed work-rate and determination during the match. Samaras then started the next match against Motherwell in the SPL and set up another goal for Anthony Stokes, Celtic went on to win the match 2–1 after being 1–0 down. Samaras went on to score his first goal of the 2011–12 season in a 5–0 win over St Mirren. Manager Neil Lennon said that; "He got his goal, which we've been waiting on a long time. His play was fantastic. He is a talent and all we are asking for is consistency. He has shown everyone today what he is capable of when he is in full flow. The rest took a leaf from his book." After an impressive performance in Celtic's 1–1 draw against Italian league leaders Udinese, fellow Serie A side Palermo expressed an interest in Samaras. He had been playing as a left midfielder in the previous few weeks, and the Daily Record said that his good form since returning to the team had helped re-ignite Celtic's season. On 24 December, Samaras started as a striker and scored twice as Celtic beat Kilmarnock 2–1.
Samaras then went on to score a vital goal for Greece against Croatia on 7 October 2011, a volley from the edge of the box with his left foot. The match finished 2–0 and the result meant that Greece qualified for the Euro 2012. Samaras played in all three of Greece's group games at Euro 2012, helping them to finish second in Group A and progress to the quarter-finals. He then played in the quarter-final tie against Germany, scoring early in the second half to level the match at 1–1, although Germany went on to win 4–2 and knock Greece out.