We assembled the great snipe blood transcriptome using data from fourteen lekking males, in order to de novo identify candidate genes related to sexual selection, and determined the expression profiles in relation to mating success. The three most highly transcribed genes were encoding different haemoglobin subunits. All tended to be overexpressed in males with high mating success. We also called Single Nucleotide Polymorphisms (SNPs) from the transcriptome data and found considerable genetic variation for many genes expressed during lekking. Among these we identified 14 polymorphic candidate SNPs that had a significant genotypic association with mating success (number of females mated with) and/or mating status (mated or not). Four of the candidate SNPs were found in HBAA (encoding the haemoglobin α-chain). Heterozygotes for one of these and one SNP in the gene PABPC1 appeared to enjoy higher mating success compared to males homozygous for either of the alleles. In a larger dataset of individuals we genotyped 38 of the identified SNPs but found low support for consistent selection since only one of the zygosities of previously identified candidate SNPs and none of their genotypes were associated with mating status. However, candidate SNPs generally showed lower levels of spatial genetic structure compared to non-candidate markers. We also scored the prevalence of avian malaria in a sub-sample of birds. Males infected with avian malaria parasites had lower mating success in the year of sampling than non-infected males. Parasite infection and its interaction with specific genes may thus affect performance on the lek.