Heading into his fourth year alongside his one-time friend turned foe, Rosberg has finished second to Hamilton in the two seasons since Mercedes' arrival as the sport's new superpower and now arguably arrives at a career crossroads entering the final season of his contract at Brackley.
The German ended 2015 on a winning run - but can he sustain that kind of form consistently when the title fight is still on?
Hamilton's arrival at Brackley in 2013 reunited a partnership - and initial friendship - which was first formed when the pair, born just five months apart in 1985, were junior karters in Mercedes' junior ranks.
It was Hamilton who stamped the early marker but Rosberg, the son of 1982 world champion Keke, was also clearly showing his worth and soon headed to single-seaters, winning the Formula BMW ADAC Championship in 2002 before moving onto the F3 Euroseries.
In 2005, he landed his big break in F1 when Williams signed him as their second test driver. The German, who was also competing in GP2, tested regularly for the team and after easily winning the inaugural title in the feeder series, he was confirmed as Williams' second driver for the 2006 season.
However, his first season in Formula 1 was a difficult one, largely due to Williams' failures rather than his own. Although Nico scored points in his very first grand prix in Bahrain and even finished the race with the fastest lap time, the rest of the season was a struggle. Only one other points-scoring finish followed as Williams-Cosworth battled with pace and reliability.
The German netted a total of 20 points during his second season while in 2008 a podium finish at the very start in Australia and one in Singapore proved the highlights of a topsy-turvy campaign.
Although there wasn't a race win for Rosberg that year, there were three podium finishes, 142 points and the honour and prestige of soundly beating his legendary team-mate - the first to ever do so in F1.
Rosberg continued to hold the advantage over his elder German compatriot in 2011, particularly in qualifying, although Mercedes failed to build on their early promise and a fifth place in China was as good as the season got for Nico.
Hamilton may have been the big-money signing for 2013, but it was Rosberg who took the team's first victory of the season in Monaco, a feat he repeated at Silverstone to take two victories to the Brit's one.
A win at the season-opener in Australia, when polesitter Hamilton retired almost immediately, gave Nico the early upper hand in the title race. Further victories in Monaco, Austria and Germany, combined with more technical setbacks for the sister Mercedes, meant Rosberg led the championship by more than a full race victory at the end of the summer.
However, the balance of power turned significantly at Spa when the pair collided while battling for the lead and Rosberg was subsequently reprimanded by Mercedes' management. The next race at Monza, when Rosberg gifted Hamilton the lead with an error at the chicane, started a run of six wins in the final seven grands prix for the Briton which propelled Lewis to the world crown.
But, having already rediscovered his qualifying edge from 2014 in the closing flyaways - he would finish the year on a career-best run of six straight poles - Rosberg beat Hamilton to the win in the final three races after the title race was over.
The question of whether or not that Hamilton-beating form was an inconsequential flash in a pan, or an omen for a stronger challenge from Rosberg in the new season, represents one of 2016's most intriguing.