Roelof was born on 3 October 1876 to Christiaan van Lennep and his second wife Charlotta Louise Küpfer.  Roelof had six siblings, and a half-sister, including Madzy, Christine, August Willem and Christiaan van Lennep, all of whom later got involved in tennis .  In 1895 he and his family founded the Hilversumsche Lawn Tennisclub in their own house.  Some years after they established three cement courts. His sister Christine was appointed the club's treasurer.  His brother August Willem won the national championships in 1903 but died young, in the age of only 24, in 1908 in London.  His sister Madzy won the ladies' doubles three consecutive times (1889?1901) and the mixed two consecutive time (1899?1900, partnering Karel Beukema) both streaks started from the inaugural championships. His brother Christiaan was the most successful amongst them winning the singles on six occasions, the doubles seven times (1904, 1905, 1907, 1908, 1912, 1916, 1923)
His breakthrough came when in 1904 he won a triple crown at the Haarlem International Championships (partnering Emilie Dolleman and J. F. Sol).  In the same month he reached the finals of the Dutch International Championships in Scheveningen with his brother Christiaan but fell to Wylie Cameron Grant and Irving Wright.  On top of that he became the triple crown national champion of the Netherlands after he copied his brother, August's singles feat from last year then claimed the doubles with Christiaan and finished the day with the mixed title partnering Louise Dolleman. Next year he was able to defend his doubles titles only losing the singles to Christiaan.
In 1909 he won the mixed national championships after a three-year hiatus partnering Loes Everts. In 1910 he regained his national doubles title alongside Gerard Scheurleer. In 1911 he booked his last national title in the doubles teaming up with Adolf Broese van Groenou. 
Roelof was a soccer supporter as well and was the founding member of the Hilversumsche Footballclub 'T Gooi in 1889, first football club in Hilversum.  He was also the director of the Tarakan Petroleum and the Kali Tello coffee estate in Jakarta at the Dutch East Indies during the 1930s.  He married twice and had three children, Sylvia, Warner and Marnix Roelof.
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