Alongside Akademisk Boldklub teammate and later Danish international Martin Albrechtsen, Løvenkrands made his debut with the Denmark under-19 national team in September 1997. He scored five goals in eight matches for the Danish under-19 national team, and was named 1998 Danish under-19 Player of the Year. He was called up for the under-21 side in March 1999, and played 12 games and scored 7 goals for the under-21s until October 2001.

Born in Hørsholm, Løvenkrands signed his first professional contract with Danish Superliga club Akademisk Boldklub (AB) in February 1998. He made his Superliga debut in July 1998, and was quickly touted as a future Danish national team player by his manager Christian Andersen. He was a part of the 1999 Danish Cup-winning AB team, though he did not play in the final against Aalborg BK.

Løvenkrands joined Scottish club Rangers for £1.3 million in June 2000. He went on to play 182 games for Rangers, winning two Scottish Premier League championships. He scored 54 goals for Rangers, including a last-minute winner against Old Firm rivals Celtic in the 2002 Scottish Cup Final. During his time at Rangers, he was often played out of position as a left winger instead of his natural position of centre forward. He played the 2005–06 season in the centre forward position, as well as on the left wing, and had his highest-scoring season at Rangers.

In August 2005, he trialled for English Premier League club Middlesbrough, but decided not to move. He started the 2005–06 season still with Rangers. He played an important role in Rangers’ run to the last 16 of the UEFA Champions League, scoring four goals during the 2005–06 campaign. In the group stage, he opened the scoring in the 3–2 win against Porto, and with his goal in the 1–1 draw against Inter Milan he secured Rangers’ progression to the knock-out round. In the round of 16, he scored in both the home and away game, though Rangers were eventually eliminated by Villarreal on the away goals rule. He netted a total of fourteen goals during the 2005–06 SPL season, the highest tally of his Ibrox career.

After six years at Rangers, his contract expired in summer 2006 and he left the club on a free transfer. Løvenkrands was reportedly in talks with a number of clubs, including Spanish club Osasuna, Roma from Italy and English side Newcastle United. He eventually signed for German club Schalke 04 on 23 May 2006, joining fellow Danish international Søren Larsen.

While at Rangers, Løvenkrands made his senior international debut under national team coach Morten Olsen, in the 13 February 2002 friendly match 1–0 win against Saudi Arabia. Having played a total four international games, he was a part of the Danish squad at the 2002 FIFA World Cup, and played one minute in the 1–1 group stage draw with Senegal. He also participated at UEFA Euro 2004, playing five minutes in the 0–3 quarter-final defeat against the Czech Republic. In his 17th national team game on 15 November 2006, he scored his first international goal in a 1–1 friendly match draw with the Czech Republic. On 10 September 2008, he played his 21st national team game in the 3–2 2010 World Cup qualification win against Portugal, whereafter his international career went on hiatus.

Løvenkrands enjoyed a successful first season at Schalke, playing as a left winger and contributing six goals and four assists. In the decisive part of the season, however, he picked up an injury and was side-lined as Schalke missed out on the Bundesliga title. Løvenkrands’ second season proved less successful. After a series of unfortunate performances without any goal, partly due to injuries, he lost his place in the starting line-up. Although fit again in February 2008, Løvenkrands did not start for Schalke under interim coaches Mike Büskens and Youri Mulder. New coach Fred Rutten chose not to employ Løvenkrands, even as Schalke struggled to remain in the race for the Bundesliga and were eliminated from the 2008–09 UEFA Cup group stage. During the winter break, Schalke announced that Løvenkrands was one of the players the club would seek to sell, and moved the player to the club’s reserve team, along with Albert Streit and Carlos Grossmüller. Having played only nine minutes for the first team in the 2008–09 season, he was finally released by the club in January 2009.

Løvenkrands joined Newcastle United on a two-week trial and soon signed a contract on 23 January 2009, with a duration until the end of the season. He made his first appearance coming on as a substitute in the 2–1 loss to Manchester City. Following another substitute appearance in the 1–1 draw against Sunderland, Løvenkrands made his first start against West Bromwich Albion on 7 February and scored Newcastle’s second goal in their 3–2 victory in the ninth minute to make it 1–2. On 4 March, he scored the opening goal against Manchester United. This was the first goal that goalkeeper Edwin van der Sar had conceded in 1,311 minutes of football, dating back to 8 November 2008. On 11 May 2009, Løvenkrands scored Newcastle’s third goal in a 3–1 victory over Middlesbrough with two games left to play. Despite the victory, Newcastle lost those last two games of the season against Fulham and Aston Villa, thus relegating them to the Championship for the 2009–10 season. He left Newcastle on 1 July 2009 after his contract with the club expired.

Løvenkrands joined Newcastle for a second spell on 1 September 2009 on a three-year contract. He was handed the number 11 shirt, formerly occupied by Damien Duff, as his previous number, 24, from his first spell at the club had been taken by Andy Carroll.

After his return to St James’ Park, Løvenkrands did not start as well as he did in his first spell and played only few games. His few appearances were on the left wing, a position he felt less comfortable in. He featured in Newcastle’s 2–0 defeat against Peterborough United in the League Cup, starting on the right wing. He later admitted to having “personal problems” and that was the reason for his frequent absence, he claimed that they were behind him and he was to fully concentrate on football. Shortly afterwards, he scored his first goal of the season in a 3–0 victory over Swansea City, his fourth goal for Newcastle. On 13 January 2010, Løvenkrands scored his first Newcastle hat-trick in a 3–0 FA Cup victory against Plymouth Argyle. He made himself available for the 18 January match against West Brom despite having just returned to Denmark upon his father’s death. He increased his tally to nine goals by heading in a José Enrique cross to put Newcastle level in a 2–2 draw and dedicated it to his late father. From January onwards, Løvenkrands’ Newcastle career picked up and he formed a strong forward partnership with Andy Carroll.

His effort in the Portugal game was praised by Morten Olsen, but following the turmoil in his Schalke career, Løvenkrands had fallen out of contention for a place in the national team by September 2009. Although talks of a recall surfaced in 2010 following his impressive form at Newcastle, Løvenkrands stated that his mind was not on the recall, and he prioritized aiding the club back to the Premier League. After Newcastle’s return to the Premier League, Løvenkrands played his first game for Denmark in over two years, coincidentally against Portugal, as part of a 1–3 defeat.

He is the younger brother of fellow footballer Tommy Løvenkrands. Their father died aged 61 on 15 January 2010 after a long illness and Løvenkrands dedicated his goal against West Bromwich Albion three days later to him. Løvenkrands has since started a charity appeal to fund research into a cure for Alzheimer’s disease, from which his father suffered during the final five years of his life.

In the 2011–12 season, Løvenkrands scored twice (a goal and a penalty) in a League Cup victory over Nottingham Forest. He added one more in the next League Cup fixture, a 4–3 extra time loss to Blackburn Rovers, scoring from the spot to push the game into its latter stages. He was sidelined for much of the season with a knee injury. He was released by Newcastle on 1 June 2012.

On 9 July 2012, Lovenkrands signed a two-year deal with Championship club Birmingham City, with an option for a further year. He was given squad number 11.

Birmingham confirmed he would be released when his contract expired at the end of the 2013–14 season. He finished his Birmingham career having scored 8 goals from 42 appearances in all competitions. Løvenkrands confirmed his retirement on 19 November 2014.

Løvenkrands returned to Rangers in May 2017 as a part-time coach in the clubs Academy.

On 13 June 2018, Løvenkrands announced he would be taking on the role of Reserve Team Coach at Rangers.